Heated under-body warming systems

ABSTRACT

A heated underbody supports including heated mattresses, heated mattress overlays and heated pads, and methods of using heated underbody supports, for therapeutic warming. The heated underbody supports include a heater assembly and a layer of compressible support material. The heater assembly includes a flexible heating element , first and second bus bars, and a temperature sensor. The flexible heating element is a conductive fabric which can be adapted to stretch into a 3-dimensional compound curve without wrinkling or folding while maintain electrical conductivity, and wherein the heating element is adapted to return to the planar shape when pressure is removed. The flexible heating element may include a fabric which is coated with a conductive or semi-conductive polymer. The heated underbody support may also include a water resistant shell which may encase the heater assembly and the compressible support material.

PRIORITY

This application claims priority to U.S. Provisional Application No.61/453,311, Heated Mattress and Heated Mattress Overlay for TherapeuticUnder-Body Warming, filed Mar. 16, 2011, the disclosure of which ishereby incorporated by reference in the entirety.

BACKGROUND

There have been many attempts at making heated mattresses and heatedmattress overlays for therapeutic patient warming. Therapeutic patientwarming is especially important for patients during surgery. It is wellknown that without therapeutic intra-operative warming, mostanesthetized surgical patients will become clinically hypothermic duringsurgery. Hypothermia has been linked to increased wound infections,increased blood loss, increased cardiac morbidity, prolonged ICU time,prolonged hospital stays, increased cost of surgery and increased deathrates.

Since the early 1990s, the standard of care for surgical warming hasbeen forced air warming blankets. Prior to that time, warm watermattresses were commonly used. The warm water mattresses went out ofcommon use because they were relatively stiff and inflexible. The stiffwater mattress negated any pressure relief that the under-laying supportmattress may have provided. As a result, the combination of pressureapplied to the bony prominences and the heat from the warm watermattress both reduced blood flow and accelerated metabolism, causingaccelerated ischemic pressure injuries to the skin (“bed sores”).Additionally, the warmed water recirculating in the warming system couldbecome contaminated with bacteria, which was especially important when aleak occurred. As a result, warm water mattresses are rarely used today.

Historically, electrically heated pads and blankets for the consumermarket have been made with resistive wire heaters. The safety ofwire-based heaters has been questionable in consumer applications.However, in the operating room environment with anesthetized patients,the possibility of hot spots caused by the wires in normal use and thefailure mode of broken heater wires resulting in sparking, arcing andfires are unacceptable. Therefore, resistive wire-based heaters arerarely used in the operating room today.

Since the mid 1990s, unsuccessful attempts have been made to makeeffective and safe heated mattresses for operating room use usingflexible, sheet-like electric resistance heaters. Sheet-like heatershave been shown to be more effective in warming patients because of theeven heat production and generally they do not cause arcing and sparkingwhen they fail.

Some existing devices employ sheet-like heaters using a polymeric fabricthat has been baked at high temperature until it becomes carbonized andis thus conductive of electricity. The carbonization process makes thefabric fragile, and therefore, it must be laminated between two layersof plastic film or fiber-reinforced plastic film for stability andstrength. The lamination process results in a relatively stiff, althoughsomewhat flexible, non-stretching, non-conforming heater. In somedevices, metal foil bus bars are attached to the heater material with anelectrically conductive adhesive or bonding composition and are thenencapsulated with polyurethane-coated nylon fabric. The result is astiff and relatively inflexible bus bar.

In some devices incorporating sheet-like heaters, temperature sensorsused for control are located directly below the uppermost surface of themattress. There is no foam or other thermal insulation between theheater and the upper surface of the mattress or the patient. This designcan cause several problems. First, the patient is laying on a relativelystiff heater without padding therebetween. Second, the heater is notstretchable and is relatively inflexible. Third, the bus bars are stiffand inflexible. Finally, the controlling temperature sensor is inthermal contact with the environment through the thin upper surfacematerial. Environmental thermal influences, such as a cold metal panlaying on top of the sensor, can drive the heater into a significantover-temperature and unsafe condition. While having the heater materialin close proximity to the patient makes sense from the heat transferpoint of view, the inflexibility and non-stretchability of the heaterand the potential of an over-temperature condition due to the exposedtemperature control sensor make this device uncomfortable andpotentially unsafe.

Other sheet-like heaters found in some existing devices use acarbon-filled electrically conductive plastic ink, printed on andlaminated between two sheets of polyester film. Copper film bus bars canbe “suspended” in the carbon-filled plastic and also laminated betweenthe two sheets of polyester film. The resulting heater and bus barassembly is relatively stiff, non-conforming and non-stretching. Becausethe heater is relatively stiff, a layer of foam which may be greaterthan 1.5 inches thick (0.25-3 inches), may be placed between the heaterand the patient. This thick layer of foam may pad the patient from thestiff heater, but it also introduces a significant thermal insulationbetween the heater and the patient, making the mattress less effectivefor patient warming. Finally, the heater elements of these devices aresimilar to flat wires and are not sheet-like. In some of these devices,the polyester film is cut out of the large spaces between the individualheater elements in order to improve flexibility which makes itimpossible to produce even heat across the surface of the pad, as itwould be with any wire heater for use in a warming pad. It is hot wherethe wire or heater element is located and cold in between.

In other devices, the heater material is a carbon impregnated plasticfilm. The film may contain greater than 50% carbon by weight. Thecarbon-laden plastic film is relatively weak and non-elastic andtherefore may be extruded or laminated onto a woven fabric for stabilityand to prevent tearing. Metal film or woven wire bus bars can be bondedto the conductive plastic with a conductive adhesive and then potted ina thick layer of plastic or laminated between sheets of plastic fordurability and strength. Such fabric-reinforced film heaters can berelatively flexible, but are not stretchable or elastic. The bus barsare relatively stiff and inflexible and totally non-stretchable. Inaddition, the adhesives and laminates can crack or delaminate orotherwise fail with repeated flexing, and bus bar failures are common inflexible heaters. Such devices can additionally include a thick layer ofhigh-loft fibrous thermal insulation placed between the heater and theupper surface of the mattress. This thermal insulation reduces theeffectiveness of the mattress for patient warming.

Electrically conductive fabric made of carbon fibers has been used asheater material in therapeutic blankets. However, carbon fiber fabrichas not been used for therapeutic mattresses. Carbon fiber fabric usedin heating elements are stabilized by laminating it between layers ofplastic film in order to keep the “slippery” fiber bundles from shiftingrandomly and altering the electrical conductivity and heat production.Additionally, the carbon fibers can fracture over time with repeatedflexing, which also changes the electrical conductivity. Fiberfracturing can be minimized by laminating the fabric between layers ofplastic film. The stiffer the resultant laminate, the more protective itis of the fibers. However, stiff heaters are not optimal when used intherapeutic heating blankets and mattresses because they can contributeto the undesirable combination of localized elevated pressure andtemperature. Finally, carbon fiber fabric may heat unevenly, resultingin “hot spots.” To prevent thermal injury, the temperature of theapplied heat from these devices must be accurately and tightlycontrolled, and if the heat production of the heater is not even,accurate control is impossible.

In summary, existing devices that incorporate electrically conductivefabric heaters are of necessity relatively stiff because of the need tolaminate them between two layers of plastic film. These laminatedheaters are somewhat flexible in that they can be deformed into a simplecurve. However, they cannot respond to pressure applied to a point ontheir surfaces and deform into three dimensional compound curvesresembling a half sphere without folding and wrinkling This is becausethese laminates do not stretch. Stretching is critical to evenlydistributed, non-wrinkling 3-dimensional deformation. Finally, theseheaters utilize bonding and laminating or potting of the bus bars to theheater material to make an electrical connection and avoid “hot” bus barfailures. The heaters become very inflexible and totally non-stretchablein the areas of the bus bars. Therefore, such laminated fabric heatershave limited utility for use in pressure-reducing therapeuticmattresses.

Conductive and semi-conductive films have been made into heater elementsby applying the film to a relatively non-stretchable fabric. Thenon-stretchable fabric carrier is important because the carbon-ladenplastic film is relatively weak and inelastic. The inelasticity isimportant to note because even if the film did not tear whilestretching, it would not return to its original planar shape when thedeforming pressure is removed.

Another existing device includes an inflatable air mattress with asingle air chamber and a heater incorporating a resistive wire heatingelement stretched across its upper surface. This device may be suitablefor home use, but the single air chamber design provides insufficientaccommodation and is relatively mechanically unstable rendering itinappropriate for surgical table use. In addition, the heater assemblyis attached to the mattress around its edges and could exhibithammocking when deformed by the weight of a patient. Hammocking refersto the undesirable effect that occurs when the heater retains a planarform because of its stiffness or is suspended from its edges like ahammock or cot.

Clearly, there is a need for conductive fabric heaters for use intherapeutic heated mattresses that are highly flexible, stretchable inat least one direction and durable without needing lamination tostabilize or protect the heater fabric. There is also a need for bus barconstruction that does not result in thick, stiff, inflexible areasalong the side edges of the heater. Then, maximally effective and safetherapeutic heated mattresses need to be designed using the stretchable,durable fabric heaters.

SUMMARY

Various embodiments include flexible and conformable heated underbodysupports including mattresses, mattress overlays, and pads for providingtherapeutic warming to a person, such as to a patient in an operatingroom setting. In various embodiments, the heated underbody support ismaximally flexible and conformable allowing the heated surface to deformand accommodate the person without reducing the accommodation ability ofany under-laying mattress, for example.

In some embodiments, the heated underbody support includes a heaterassembly and a layer of compressible material. The heater assembly mayinclude a heating element including a sheet of conductive fabric havinga top surface, a bottom surface, a first edge and an opposing secondedge, a length, and a width. the conductive fabric may include threadsseparately and individually coated with an electrically conductive orsemi-conductive material, with the coated threads of the fabric beingable to slide relative to each other such that the sheet is flexible andstretchable. The heater assembly may also include a first bus barextending along the entire first edge of the heating element and adaptedto receive a supply of electrical power, a second bus bar extendingalong the entire second edge of the heating element, and a temperaturesensor. The layer of compressible material may be adapted to conform toa person's body under pressure from a person resting upon the supportand to return to an original shape when pressure is removed. It may belocated beneath the heater assembly and may have a top surface and anopposing bottom surface, a length, and a width, with the length andwidth of the layer being approximately the same as the length and widthof the heater assembly.

In some embodiments, the conductive or semi-conductive material ispolypyrrole.

In some embodiments the compressible material includes a foam materialand in some embodiments it includes one or more air filled chambers. Insome embodiments, the heated underbody support also includes a waterresistant shell encasing the heater assembly, including an upper shelland a lower shell that are sealed together along their edges to form abonded edge, with the heater assembly attached to the shell only alongone or more edges of the heater assembly. In some embodiments, theheating element has a generally planar shape when not under pressure, isadapted to stretch into a 3 dimensional compound curve without wrinklingor folding while maintaining electrical conductivity in response topressure, and to return to the same generally planar shape when pressureis removed.

In some embodiments, the heated underbody support includes a heaterassembly including a flexible heating element comprising a sheet ofconductive fabric having a top surface, a bottom surface, a first edgeand an opposing second edge, a length, and a width, a first bus barextending along the first edge of the heating element and adapted toreceive a supply of electrical power, a second bus bar extending alongthe second edge of the heating element, and a temperature sensor. Theheating element may have a generally planar shape when not underpressure, and, in response to pressure, may be adapted to stretch into a3-dimensional compound curve without wrinkling or folding whilemaintaining electrical conductivity, and then to return to the samegenerally planar shape when pressure is removed. The underbody supportmay further include a layer of compressible support material locatedbeneath the heater assembly which conforms to a patient's body underpressure and returns to an original shape when pressure is removed.

In some such embodiments, the heating element includes a fabric coatedwith a conductive or semi-conductive material, which may be a carbonfiber or metal containing polymer or ink, or may be a polymer such aspolypyrrole. In some embodiments, the heated underbody support alsoincludes a shell including two sheets of flexible shell surrounding theheater assembly, the shell being a water resistant plastic film or fiberreinforced plastic film with the two sheets sealed together near theedges of the heater assembly. In some embodiments, the heated underbodysupport also includes a power supply and controller for regulating thesupply of power to the first bus bar.

In some embodiments, the compressible material comprises one or moreflexible air filled chambers. In some such embodiments, the compressiblematerial is a foam material. The heater assembly may be attached to thetop surface of the layer of compressible material. In some embodiments,the heated underbody support includes a water resistant shell encasingthe heater assembly and having an upper shell and a lower shell that aresealed together along their edges to form a bonded edge. In some suchembodiments, one or more edges of the heater assembly may be sealed intothe bonded edge. In some embodiments, the heater assembly is attached tothe upper layer of water resistant shell material. In some embodiments,the heater assembly is attached to the shell only along one or moreedges of the heater assembly. In some embodiments, the heated underbodysupport also includes an electrical inlet, wherein the inlet is bondedto the upper shell and the lower shell and passes between them at thebonded edge.

In some embodiments, the heating element has a first Watt density whenin a generally planar shape and a second Watt density when stretchedinto a 3 dimensional shape such as a compound curve, with the first Wattdensity being greater than the second Watt density. In some embodiments,the temperature sensor is adapted to monitor a temperature of theheating element and is located in contact with the heating element in asubstantially central location upon which a patient would be placedduring normal use of the support. In some embodiments, the heatedunderbody support also includes a power supply and a controller forregulating a supply of power to the first bus bar.

In some embodiments, the heated underbody support is a heated mattressand includes a heater assembly and a layer of compressible materialwhich conforms to a patient's body under pressure and returns to anoriginal shape when pressure is removed located beneath the heaterassembly. The layer of compressible material may include one or moreinflatable chambers positioned under the heater assembly. A flexible,water resistant cover may encase the heater assembly, the layer ofcompressible material and the inflatable chambers. The heater assemblymay include a flexible heating element including a sheet of conductivefabric having a top surface, a bottom surface, a first edge and anopposing second edge, a length, and a width, a first bus bar extendingalong the first edge and adapted to receive electrical power from apower supply, a second bus bar extending along the second edge, and atleast one temperature sensor. The heating element may have a generallyplanar shape when not under pressure, may stretch into a 3-dimensionalcompound curve without wrinkling or folding while maintain electricalconductivity in response to pressure, and may return to the generallyplanar shape when pressure is removed.

In some embodiments, the heated underbody support may also include oneor more additional inflatable chambers positioned under the layer ofcompressible material, with each of the inflatable chambers beingelongated, having a longitudinal axis and being positioned side-by-sideone another with their longitudinal axes extending substantially fromthe first end to the second end of the support. In some embodiments, theinflatable chambers can be inflated and deflated in two groups while thesupport is in use, with the inflatable chambers being in alternatinggroups such that each inflatable chamber is in a different group fromeach inflatable chamber which is beside it.

In some embodiments, the heated underbody support includes a pluralityof additional inflatable chambers. In some embodiments, the inflatablechambers can each be inflated and deflated independently while thesupport is in use. In some embodiments, the inflatable chambers can allbe inflated and deflated simultaneously as a group while the support isin use. In some embodiments, the inflatable chambers can be inflated anddeflated in two or more groups while the support is in use. In someembodiments, each of the chambers belongs to one of two or more groups,and the support includes separate conduits to each group with eachconduit providing independent fluid communication one groups ofinflatable chambers for independently introducing or removing air fromthat group of inflatable chambers.

In some embodiments, the heated underbody support also includes apressure sensor for measuring an actual internal air pressure of thegroups of inflatable chambers, and a controller including a comparatorfor comparing a desired internal air pressure for each group ofinflatable chambers with the actual internal air pressure of each groupinflatable chambers. The controller may be operatively connected to eachof the conduits and to an air pump and may further including or beoperatively associated with a pressure adjusting assembly for adjustingthe actual internal pressure. The controller may be adapted to causeinflation or deflation of each group of inflatable chambers to adjustthe actual internal air pressure of each of the group of inflatablechambers toward the desired internal air pressure. In some embodiments,each inflatable chamber within each group of inflatable chambers is influid connection with every other inflatable chamber of its own group sothat air pressure changes in one inflatable chamber redistribute to allof the other inflatable chambers in the same group. In some embodiments,an interface pressure is maintained on a top surface of each group ofchambers at a location which supports a patient's body during normaluse, the interface pressure being below a capillary occlusion pressurethreshold of 32 mm Hg. Some embodiments include methods of warming aperson using any of the heated underbody supports described herein. Insome embodiments, the method includes positioning the person on theheated underbody support, activating the support, and directing thesupport to maintain a desired temperature. The heated underbody supportmay include a heater assembly, a layer of compressible material locatedbeneath the heater assembly, and a flexible water resistant shellencasing the heater assembly. The heater assembly may include a flexibleheating element including a sheet of conductive fabric having a topsurface, a bottom surface, a first edge and an opposing second edge, alength, and a width, a first bus bar extending along the first edge andadapted to receive a supply of electrical power, a second bus barextending along a second edge, and a temperature sensor on or near theheating element. The heating element may have a generally planar shapewhen not under pressure, and may, in response to pressure from theperson positioned on the support, stretch into a 3 dimensional compoundcurve without wrinkling or folding while maintain electricalconductivity.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments andtherefore do not limit the scope of the invention. The drawings are notto scale (unless so stated) and are intended for use in conjunction withthe explanations in the following detailed description. Variousembodiments will hereinafter be described in conjunction with theappended drawings, wherein like numerals denote like elements.

FIG. 1 is a cross sectional view of a heater assembly undergoingdeformation in accordance with some embodiments.

FIG. 2 is a cross sectional view of a heater assembly in accordance withsome embodiments.

FIG. 3 is an illustration of a heater assembly in accordance with someembodiments.

FIG. 4 is an illustration of a power connection portion of a heaterassembly in accordance with some embodiments.

FIG. 5 is an illustration of a heater assembly in accordance with someembodiments.

FIG. 6 is a cross sectional view of a heated mattress overlay or pad inaccordance with some embodiments.

FIG. 7 is a cross sectional view of a heated mattress overlay or pad inaccordance with some embodiments.

FIG. 8 is a cross sectional view of a heated mattress overlay or pad inaccordance with some embodiments.

FIG. 9 is an illustration of a heated mattress overlay or pad inaccordance with some embodiments.

FIG. 10 is a cross sectional view of a heated mattress overlay or pad inaccordance with some embodiments.

FIG. 11 is a cross sectional view of a heated mattress overlay or pad inaccordance with some embodiments.

FIG. 12 is a cross sectional view of a heated mattress overlay or pad inaccordance with some embodiments.

FIG. 13 is a cross sectional view of a heated mattress overlay or padwith partial thickness cuts or channels in the foam layer in accordancewith some embodiments.

FIG. 14 is an illustration of a heated mattress overlay or pad with asegmented foam layer in accordance with some embodiments.

FIG. 15 is a cross sectional view of a heated mattress overlay or padwith a contoured foam layer in accordance with some embodiments.

FIG. 16 is an illustration of a heated mattress overlay or pad with afoam ring by the temperature sensor assembly in accordance with someembodiments.

FIG. 17 is a cross sectional view of a heated mattress overlay or padwith a foam ring surrounding the temperature sensor assembly inaccordance with some embodiments.

FIG. 18 is a cross sectional view of a heated mattress overlay or padwith a foam ring surrounding the temperature sensor assembly inaccordance with some embodiments.

FIG. 19 is a flow diagram showing the operation of a heater assembly inaccordance with some embodiments.

FIG. 20 is a cross sectional view of a heated mattress overlay or padwith a thin foam layer located above the heater element assembly inaccordance some embodiments.

FIG. 21 is an illustration of a heated mattress overlay or pad with athin upper foam layer with a plurality of apertures in accordance someembodiments.

FIG. 22 is a cross sectional view of a heated mattress overlay or padwith a power entry assembly located in the peripheral bond between theshell layers in accordance some embodiments.

FIG. 23 is an illustration of a heated mattress overlay or pad withattachment tabs in accordance with some embodiments.

FIG. 24 is an illustration of a strap and a heated mattress overlay orpad with attachment tabs in accordance some embodiments.

FIG. 25 is a cross sectional view of a heated mattress including avisco-elastic foam layer in accordance with some embodiments.

FIG. 26 is a cross sectional view of a heated mattress including aninflatable chamber in accordance with some embodiments.

FIG. 27 is a cross sectional view of a heated mattress includingplurality of inflatable chambers in accordance with some embodiments.

FIG. 28 is a cross sectional view of a heated mattress including aplurality of inflatable chambers in accordance with some embodiments.

FIG. 29 is a schematic diagram of a console in accordance with someembodiments.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description providespractical illustrations for implementing various exemplary embodiments.Examples of constructions, materials, dimensions, and manufacturingprocesses are provided for selected elements, and all other elementsemploy that which is known to those of skill in the field. Those skilledin the art will recognize that many of the examples provided havesuitable alternatives that can be utilized.

Embodiments include heated underbody supports which include heatedmattresses, heated mattress overlays, and heated pads. The termunderbody support may be considered to encompass any surface situatedbelow and in contact with a user in a generally recumbent position, suchas a patient who may be undergoing surgery, including heated mattresses,heated mattress overlays and heated pads. Heated mattress overlayembodiments may be identical to heated pad embodiments, with the onlydifference being whether or not they are used on top of a mattress.Furthermore, the difference between heated pad embodiments and heatedmattress embodiments may be the amount of support and accommodation theyprovide, and some pads may be insufficiently supportive to be used alonelike a mattress. As such, the various aspects which are described hereinapply to mattresses, mattress overlay and pad embodiments, even if onlyone type of support is shown in the specific example.

Various embodiments improve patient warming effectiveness by increasingaccommodation of the patient into the heated mattress, mattress overlay,or pad, in other words, by increasing the contact area between thepatient's skin and the heated surface of the mattress or mattressoverlay. The heating element, and the foam or air bladders of themattress, which may also be included, are easily deformable to allow thepatient to sink into the mattress, mattress overlay, or pad. Thisaccommodation increases the area of the patient's skin surface incontact with the heated mattress, mattress overlay, or pad and minimizesthe pressure applied to the patient at any given point. It alsoincreases the surface contact area for heat transfer and maximizes bloodflow to the skin in contact with the heat for optimal heat transfer. Theaccommodation of the patient into the mattress, mattress overlay, or padis not hindered by a stiff, non-conforming, non-stretching, hammockingheater. Additionally, in various embodiments, the heating element is ator near the top surface of the underbody support, in thermallyconductive contact with the patient's skin, not located beneath thicklayers of foam or fibrous insulation.

Various embodiments further provide improved safety. For example, someembodiments provide a heating element that does not produce or reduces“pressure points” against the patient's body, such as against bonyprominences, which can occur when a heater is stiff. In addition,various embodiments can reduce or prevent thermal “grounding” of thetemperature control sensor. Various embodiments can provide an automaticreduction in Watt density in areas of maximum loading and deformationthat correspond to areas of maximum pressure. In some embodiments, ifthe heater assembly eventually fails, it fails “cool” (stops heating)rather than failing “hot” and risking an injury or fire.

In certain embodiments, the heater assembly includes a heating elementmade of a conductive material. The conductive material may bestretchable in at least one direction or, alternatively, in at least twodirections. One way to create a stretchable fabric heating element is tocoat a conductive material onto individual threads or fibers of acarrier fabric which may be a non-conductive material. The threads orfibers may be woven or knitted, for example, into a stretchable fabric.Other examples of conductive fabrics which may be employed include,without limitation, carbon fiber fabrics, fabrics made from carbonizedfibers, and woven or non-woven substrates coated with a conductivematerial, for example, polypyrrole, carbonized ink, or metalized ink.

The conductive material may be applied to the fibers or threads beforethey are woven or knit into a fabric. In this way, the coated threadscan move and slide relative to each other as the fabric is stretched,and can return to their original orientation when the stretching isstopped such that the fabric can return to its original shape.Alternatively, the conductive materials that coat the individual fibersin the fabric may be applied after the fabric is woven or knit using adipping, spraying, coating or polymerization process or combinationsthereof. A conductive polymer can be selected that coats to theindividual threads without bonding them together such that the threadsremain able to slide relative to each other.

Types of materials which may be used for the fabric base include naturaland synthetic materials such as polyurethane-polyurea copolymer (forexample spandex or Lycra made by INVISTA, Wichita, Kans., polyester,polyamide, (for example Nylon) or combinations thereof. The material maybe elastic in nature such that the threads or fibers can stretch andthen return to their original size or length. Alternatively oradditionally, stretch and elasticity may be provided by the manner inwhich the threads or fibers are knit or woven, such as by forming atwill weave. Alternatively or additionally, stretch and elasticity maybe provided by the manner in which fibers or groups of fibers aretwisted or combined prior to being knit or woven into fabric.Alternatively, or additionally, the stretch and elasticity may beprovided by the structure introduced to the fabric through shaping ofthe physical structure or shape of the fabric such as by embossing,creping or other mechanical means. Alternatively or additionally stretchand elasticity may be provided by the use of stretchable polymer orfibers in a nonwoven fabric.

The conductive coating may be applied to the individual fibers orthreads before or after forming a fabric by spraying, coating ordipping, for example. Various conductive materials may be used. Examplesinclude conductive and semi-conductive polymers include polypyrrole,polyaniline and polyacetylene.

In some embodiments, in contrast to non-stretchable conductive filmheaters, where a carbon (or other conductive material) impregnatedplastic film is extruded onto or bonded onto a base layer such as afabric base layer, the heating element material may have a conductive orsemi-conductive material coated onto the individual threads or fibers ofthe carrier fabric. This maintains the natural flexibility andstretch-ability of the fabric rather than turning the fabric into anon-stretchable fiber reinforced film.

The conductive or semi-conductive coating may comprise a polymer that isbound as a layer surrounding the individual threads or fibers by aprocess of polymerization. Polymerization results in a very secure bond.Embodiments of the flexible coating on each individual thread or fibermay not crack, fracture or delaminate during flexion. Polymerization ofthese conductive or semi-conductive materials onto individual fibers ofthe carrier fabric is one example of a process for producing a durable,flexible and stretchable heater assembly according to variousembodiments. Semi-conductive polymer coatings such as polypyrrole areuseful in various embodiments, however, other coating processes areanticipated and conductive coatings that use carbon or metal as theconductive material are also anticipated.

The electrically conductive or semi-conductive fabric heater materialsused in heating elements may be highly flexible and durable such thatneither the carrier fiber nor the semi-conductive polymer coating willfracture with repeated flexing, loading and stretching. Additionally,the conductive or semi-conductive fabric heating element does notrequire lamination between layers of plastic film for protection orstabilization, though it may be laminated if desired.

The conductive fabric heating element material may be highly flexibleand conformable, allowing the heated surface to comfortably deform andaccommodate the patient. To accomplish this, the heater assembly has aflexible, electrically conductive fabric heating element that may bemade of woven or knit fabric that can stretch in at least one direction.The fabric heating element may be durable without requiring laminationbetween plastic film sheets for stabilization and protection, though insome embodiments the heating element may be laminated. In someembodiments, the flexible and conformable fabric heating element can beincluded in a mattress overlay and can be positioned directly againstthe plastic film of the upper surface of a mattress with which it isused without requiring a foam pad there between, or alternatively a foampad may be included beneath the heating element. Furthermore, with nofoam or thermal insulation layer between the heating element and thepatient, heat transfer from the heating element to the patient ismaximized.

The heating element comprises a flexible flat sheet of the conductivematerial. In some embodiments, it is rectangular having opposing firstand second edges and opposing third and fourth edges extending from thefirst to second ends, a first planar surface and an opposing bottomplanar surface. According to some embodiments, the heating element alsoincludes closely spaced conductive elements such that the heatingelement has a substantially uniform Watt density output, in someembodiments less than approximately 0.5 watts/sq. inch, such as betweenapproximately 0.1 and approximately 0.4 watts/sq. inch, of one or bothsurfaces, across a portion of or the entirety of the surface includingand extending to the edges of the heating element. The closely spacedelements can be conductive threads woven into the fabric or conductivematerials such as conductive ink applied to the fabric.

According to an exemplary embodiment, a conductive fabric comprising theheating element comprises woven polyester fibers individually coatedwith polypyrrole (available from Eeonyx Inc., Pinole, Calif.). Thecoated fabric may have an average resistance, for example, determinedwith a four point probe measurement, of approximately 15-20 ohms persquare at about 48 volts, which is suitable to produce a Watt density ofapproximately 0.1 to approximately 0.4 watts/sq. in. for the surface ofthe heating element, when the heating element has a width between thebus bars in the neighborhood of about 16-28 inches, though wider andnarrower heater element widths are also contemplated. Such widths aresuitable for a mattress, mattress overlay, or pad heating assembly, someembodiments of which will be described below. The resistance of such aconductive fabric may be tailored for different widths between bus bars(with wider requiring a lower resistance and narrower requiring a higherresistance) by increasing or decreasing a surface area of the fabricthat can receive the conductive coating, for example, by increasing ordecreasing the basis weight of the fabric. Resistances over surfaceareas of conductive fabrics such as these may vary, for example, due tovariation in a thickness of a conductive coating, variation within theconductive coating itself, variation in effective surface area of thesubstrate which is available to receive the conductive coating, orvariation in the density of the substrate itself. Local surfaceresistance across a heating element is directly related to heatgeneration according to the following relationship: Q(Joules)=I²(Amps)×R(Ohms). Variability in resistance thus translatesinto variability in heat generation, which is measured as a temperature.Precise temperature control can be maintained in embodiments which areemployed to warm patients undergoing surgery, for example.

The stretchable fabric heating element is able to deform in response toa focal pressure applied to the surface of the heater fabric, into asmooth 3-dimensional compound curve without wrinkling or folding. Asmooth compound curve cannot be formed out of non-stretchable fabrics orfilms. The stretchable fabric heating element may also exhibit elasticproperties that allow it to revert to its original planar shape when thedeforming pressure is relieved. The fabric heating element can beprovided with appropriate tensile properties such that the amount ofstretch, or strain, required to prevent hammocking and allowaccommodation of the patient into the heated mattress or mattressoverlay does not result in stresses that exceed the elastic limit of thematerial. In some embodiments, for example, an increase in the width ofa 20 inch wide mattress or mattress overlay of approximately one inchduring stretching achieves the desired goals without exceeding theelastic limit of the stretchable fabric heating element or introducingpermanent plastic deformation.

An example of a heater assembly 1 including a stretchable fabric heatingelement 10 is shown in FIG. 1, which depicts a cross section of aportion of the heater assembly 1. This example includes a heatingelement 10, a compressible material layer 20 beneath the heating element10 and bonded to the heating element 10 by a layer of adhesive 30. Theheater assembly 1 also includes an upper shell 40 and a lower shell 42.The heater assembly 1 curves smoothly under pressure from a patient'sbody (not shown) to stretch into an area of compound curve deformation22.

In the embodiment shown in FIG. 1 and in several other embodiments, afoam layer 20 is included beneath the heating elements 10. However, thecompressible material layer 20 may alternatively be described as a layerof foam in each of these embodiments but is not limited to foam. Forexample, the layer of compressible material may comprise gel, stuffingmaterial such as polyester, polyester pellets, bean bag material such aspolystyrene beads, air filled compartment, or any material that providesa flexible layer for patient accommodation.

Heat transfer is maximized when the heating element 10 is in conductivethermal contact with the patient. However, in some embodiments, at leastone layer of plastic film is interposed between the heating element 10and the patient to protect the heating element 10. One or more layers ofthin plastic film may form an upper shell 40 between the heating element10 and the patient to introduce minimal thermal resistance to heat flow.In certain embodiments the fabric heating element 10 may be laminatedbetween two layers of thin (such as less than 0.003 inches) plasticfilms (e.g. urethane or polyvinyl chloride) that may also be stretchy.Laminating a thin layer of plastic film directly onto each side of theheating element 10 protects the heating element fabric from damage byliquids and oxidation. Thin layers of plastic film are sufficient toprotect the heating element 10 from liquid and gases, add minimal if anystiffness to the construction, and still allow the heating element 10 tostretch and return to its original shape. This is in contrast to someother conductive fabrics which require lamination between two thicklayers of plastic film in order to provide structural strength anddurability, resulting in a stiff and non-stretchable heater.

The heating element 10 can stretch in at least one dimension and in someembodiments in two dimensions, such that it can easily deform from aflat planar surface to a half sphere type of formation when loaded withthe weight of a patient, particularly of a bony prominence. Since theheat output of the heating element 10 is constant, the heat output perarea (Watt density) will decrease as an area of the heating elementmaterial is stretched, for example, from a planar shape such as a circleinto a three dimensional shape such as a half sphere, by the weight ofthe patient's body or body part. For example, the area of a circle isπr², while the area of a half sphere is 2πr² and is therefore double.Therefore, in some embodiments the Watt density of the heater isnaturally and automatically reduced by up to approximately half in theload-bearing areas as the heater material stretches from the twodimensional shape such as a circle into a three dimensional shape suchas substantially a half sphere. This reduction in Watt density due tothe increase in surface area caused by stretching results in anautomatic, inherent decrease in temperature of the heating element underthe points of increased pressure.

The pressure relief provided by the underbody support is maintained byallowing maximal accommodation (allowing the patient to sink into thesupport) without the heater creating a “hammocking” force. By allowingmaximal accommodation and avoiding hammocking, cutaneous blood flow ismaximized at the pressure points which minimizes the risk of pressureulcers. The pressure needed to collapse capillaries is said to be 32 mmHg. By allowing maximal accommodation and avoiding hammocking, cutaneousblood flow is generally maximized. By maximizing blood flow, the abilityof the skin and tissue to absorb heat from the heating element andtransfer it to the rest of the body is also maximized. Further, byallowing the patient to sink into the underbody support (accommodation),the surface area of the heating element 10 in contact with the patientis maximized and thus heat transfer is maximized.

Mattresses used in the operating room typically have a useful life spanof 5-15 years. Flexible, conductive fabric heaters may be expected tofail in less than 10 years. In prior art heaters, the failure is usuallyat the bus bar/fabric heater connection, and will usually result in a“hot spot” which can cause burning of the patient. For example, carbonand metal based conductive fabrics and films retain relative stabilityof their conductivity over time and it is therefore hot failure mayoccur.

Some materials such as semi-conductive materials used to createconductive fabric heating elements in certain embodiments, such aspolypyrrole, slowly lose their electrical conductivity over time.Oxidation of the semi-conductive material can cause the electricalresistance of the heating element to increase in some instances, such asby approximately 10% per year during normal use. Therefore, in someembodiments, the controller is electrically connected to the heatingelement and bus bars such that it can measure resistance. In someembodiments, the controller a regulates the power supply to the heatingelement and can be programmed to check the total resistance of theheating element 10 periodically, such as before each use. If theresistance of the heating element 10 eventually increases over time to apredetermined level set as a cut off point, an alarm may be triggeredand the controller may cease to energize the heating element 10. Thissafety feature allows the heated underbody support to fail safely, or“cold,” without hot spots, and therefore without risking burning thepatient, before a mechanical failure. Such a safe failure is in contrastto a bus bar delamination, for example, which can cause an unsafe, or“hot,” failure.

Other types of failures may occur over time in heater assembliesincluding flexible, conductive fabric heating elements 10 and someembodiments can plan for such failures to mitigate or eliminate anyassociated risk. For example, failures may occur at the bus bar/heatingelement 10 connection, or alternatively may result from a failure of theheating element material itself, such as a tear or fractured fibers orthreads or thread coating. In any of these examples, the failure couldresult in a “hot spot,” or localized area running at a temperaturegreater than intended. Therefore, a heated mattress or mattress overlaythat utilizes a heating element 10 comprising a conductive material thatis electrically stable and does not loose electrical conductivity overtime may be kept in service until it experiences a mechanical failurethat results in a “hot spot” that could injure a patient. This eventualfailure can be prevented through planned obsolescence. To prevent hotfailures, certain embodiments include planned obsolescence, achieved bythe gradual degradation of the electrical conductivity of the heaterelement and monitoring of resistance as described above. This safetyfeature results in a cold failure with no potential for patient injury,before any hot failures are likely to occur. This planned obsolescenceis therefore a safety feature in that the mattress fails cold, before amechanical failure, such as a bus bar delamination, could cause a hotfailure. The resistance cut off point may be set by the manufacturer,for example, as being a resistance level that the conductive fabric isexpected to reach prior to mechanical failure during normal use. Forexample, the resistance cut off may be between about 125 percent andabout 300 percent of the original resistance value, such as when thesupport was new or when the support was first used. Alternatively, theresistance cut off value may be the resistance at which the support willproduce less than a certain number of Watts per square inch of heatedspace, such as less than between about 0.04 and about 0.15 Watts persquare inch. Planned obsolescence is therefore a useful safety featurebecause it results in cold failure and no patient injury.

In certain embodiments, the conductive or semi-conductive fabric heatingelement 10 is made into a heater assembly 1 by attaching two electricalconductors, or bus bars, along opposing ends of the fabric heatingelement 10. The bus bars of some embodiments may be attached to theheating element material by sewing with electrically conductive thread.This construction maintains flexibility and durability with repeatedflexing. The sewn connection between the bus bar and the heating elementfabric according to embodiments results in a connection that is veryrobust, flexible and tolerant of extreme flexing and resistant todegradation.

According to some embodiments, the bus bars are coupled to the heater bya stitched coupling, for example, formed with electrically conductivethread such as silver-coated polyester or nylon thread (Marktek Inc.,Chesterfield, Mo.), extending through the conductive fabric material andthrough the bus bars. Alternative threads or yarns employed by someembodiments may be made of other polymeric or natural fibers coated withother electrically conductive materials. In addition, nickel, gold,platinum and various conductive polymers can be used to make conductivethreads. Metal threads such as stainless steel, copper or nickel couldalso be used for this application. According to an exemplary embodiment,the bus bars are comprised of flattened tubes of braided wires; forexample, a flat braided silver coated copper wire, and may thusaccommodate the attaching thread extending there through, passingthrough openings between the braided wires thereof. In addition, suchbus bars are flexible, thereby enhancing the flexibility of the mattressheater assembly. According to alternate embodiments, the bus bars can bea conductive foil or wire, flattened braided wires not formed in tubes,an embroidery of conductive thread, a printing of conductive ink, orother suitable bus bar construction. The bus bars may comprise a flatbraided silver-coated copper wire material, since a silver coating hasshown superior durability with repeated flexion, and is less susceptibleto oxidative interaction with a polypyrrole coating of the heatingelement 10. Additionally, an oxidative potential due to dissimilarmetals in contact with one another is reduced if a silver-coated threadis used for the stitched coupling of a silver-coated bus bar.

According to some embodiments, two or more rows of stitches are appliedto each bus bar for added safety and stability of the bus bar/heatingelement 10 interface. Two rows of stitches may be used and may beoriented in a pattern such as a “zigzag” pattern so that each row ofstitches captures or extends back and forth across each longitudinaledge of the bus bar and onto the heating element, along the length ofthe bus bar where it abuts the heating element. A zigzag pattern ofrelatively closely positioned stitches stabilizes the flexible fabricheating element 10 and holds it in close opposition to the bus bar sothat the fabric heating element cannot physically pull away from the busbar during flexing. According to some additional embodiments, a ribbonof highly conductive material is interposed between the bus bar and thefabric heater element. For example, a ribbon or strip of cloth that hasbeen coated with a conductive metal such as silver may be used. Thecloth ribbon may be soft, flexible and fibrous or bristly and,therefore, the fibers or bristles may integrate themselves into thespaces within the materials of the bus bars and/or of the fabric heaterelement. Other embodiments comprising options for improving theelectrical connection between the bus bar and the fabric heating element10 include a layer of highly conductive paint or ink, selectivelyapplied to the conductive fabric of the heating element 10 and to whichthe bus bar is attached rather than the bus bar being attached directlyto the conductive fabric of the heating element 10.

FIG. 2 depicts a side view of a heater assembly 1 and a stitched bus barconstruction according to some embodiments. It includes a heatingelement 10, a first bus bar 62 at a first end 12 of the heating element10 and a second bus bar 64 at a second end 14 of the heating element 10.A first insulating member 72 is located between first end 12 and firstbus bar 62 and a second insulating member 74 is located between secondend 14 and second bus bar 64. Conductive thread 80 connects the heatingelement 10 to the bus bars 62, 64 through the insulating members 72, 74.In this way, the electrical contact points between the bus bars 62, 64and the heating element 10 may be solely defined by the conductivethread 80 of the stitched couplings.

Insulating members 72, 74 may be fiberglass material strips having anoptional polytetrafluoroethylene (PTFE) coating and a thickness ofapproximately 0.003 inch, for example. Alternatively, electricallyinsulating members 72, 74 could be comprised of a polymeric film, apolymeric film reinforced with a fibrous material, a cellulose material,a glass fibrous material, rubber sheeting, polymeric or rubber-coatedfabric or woven materials or any other suitable electrically insulatingmaterial.

The use of conductive thread stitches 80 of the coupling maintains astable and constant contact with the bus bar 62, 64 on one side and theheating element 10 on the other side of the insulator 72, 74.Specifically, the stitches can produce a stable contact in the face ofany degree of flexion, so that the potential problem of intermittentcontact between the bus bar 62, 64 and the heating element 10 (thatcould arise in embodiments where the bus bar relies upon direct physicalcontact between the surface of the bus bar with the surface of theheating element) can be avoided. The stitching 80 comprises theelectrical connection between the bus bar 62, 64 and the heating element10, and by using a conductive thread that has a lower electricalresistance than the conductive fabric of the heating element 10, thethread does not generate significant heat under normal conditions. Inaddition to the heated mattress, mattress overlay, and pad applicationsdescribed herein, such a design for providing for a uniform and stableconductive interface between a bus bar and a conductive fabric materialcan be used to improve the conductive interface between a bus bar or anelectrode and a conductive fabric in non-flexible heaters, in electronicshielding, in radar shielding, in mats for pressure measuring andmapping and in other applications of conductive fabrics.

Due to the flexible nature of the heating element 10 in certainembodiments of the heater assembly 1, the thread of a stitched couplingbetween the heating element 10 and the bus bar may 62, 64 undergostresses that, over time and with multiple uses of an underbody supportcontaining the heater assembly 1, could lead to one or more fracturesalong the length of the stitching 80. Such a fracture could also resultin intermittent contact at points between the bus bar 62, 64 and theheating element 10, which could lead to a thermal melt down of theelement 10 along the bus bar 62, 64. But, if such a fracture were tooccur with an insulating member 72, 74 positioned between the bus bar62, 64 and the heating element 10, the insulating member 72, 74 mayprevent a meltdown of the heating element 10, so that only the verysmall area of the heating element material directly in contact with theconductive thread of the stitching 80 melts along the bus bar 62, 64with a very small spot of excessive heat insufficient to cause an injuryto a patient. The “hot area” is limited to an area approximately 2-4 mmin diameter at any time. The “hot area” may move down the bus bar 62, 64as the heating element fails but at any given time the “hot area” islimited to a very small area.

In some embodiments, the stitched coupling between the bus bar 62, 64and the heating element 10 comprises two or more rows of stitches 80 forredundancy and stability. In other embodiments, a single row may beused. The stitching 80 may extend along substantially the entire end 12,14 of the heating element 10.

An aerial view of an embodiment of a heater assembly 1 is shown in FIG.3, in which the bus bars 62, 64 extend past the ends 16, 18 of theheating element 10. If the ends of bus bars 62, 64 do not extend atleast to the ends 16, 18 of the heating element 10, increased currentcan flow from the ends of the bus bars and into the heating element. Inrectangular heater assemblies 1, the current flows approximatelyperpendicularly between the bus bars 62, 64, therefore, each point onone of the bus bars 62, 64 in effect supplies a narrow line of currentto the other of the bus bars 62, 64. If either bus bar terminates beforereaching the end of the heating element, excessive current can flow outthe end of that bus bar. The excess current flow at that point canresult in excessive heating of the heating element adjacent the end ofthat bus bar, which can cause a hot spot and degradation of the fabricleading to a failure of the heating element. To avoid such a failure andto improve manufacturing reliability, by avoiding the inadvertentmanufacturing error of the bus bar not extending to the ends of theheating element 10, both ends of the bus bars 62, 64 are extended beyondthe ends 16, 18 of the heating element 10, such as by a length of atleast approximately 0.060″. In certain embodiments, the conductivethread stitches 80, previously described, also extend past the ends 16,18 of the heating element 10, being terminated on the bus bar extensions66. This design advantageously creates an easy manufacturing process,which assures a dependable and repeatedly manufacturable bus bartermination that avoids the creation of hot spots at the ends of the busbars 62, 64.

In some embodiments, the power connection between the power source andthe heater is located at a portion of the bus bar 62, 64 that is nottouching the fabric heating element 10. For example, in someembodiments, the bus bars 62, 64 extend beyond the end of the heatingelement 10, such as by about 1 to 2 inches, and the power lead issoldered to the bus bar extension 66 such that it is spaced away fromand is not physically touching the heating element 10. Such a locationof the solder joint of this power connection may make the connectionless susceptible to stress and breaking Other ways of connecting thepower lead to the bus bar extension 66 include, but are not limited to,crimping, weaving, or riveting.

Power lead electrical connections according to some embodiments are madea short distance off of the heating element 10 in order to improve busbar 62, 64 durability and avoid creating uncomfortable lumps. Also, theuse of solder connections and rivets are avoided in some embodiments. Aclose-up view of a power connection portion of a heater assembly isshown in FIG. 4. A short length of conductive material, such as a shortpower connection “tail” 90 of woven wire bus bar material, is partiallyinserted inside an inner lumen of the flattened tube of a woven wire busbar 60 and sewn to the bus bar 60 and the heating element 10 when thebus bar 60 is stitched (not shown) to the heating element 10. Thisstitched mechanical connection between the tail 90 and the bus bar 60retains full flexibility of the woven bus bar 60 because there is nosolder. The power connection to the bus bar 60 can then be made bysoldering the power lead 100 to the other end of the tail 90 that is notphysically touching the heating element 10. Other means of connectingthe power lead to the bus bar extension include, but are not limited to,crimping, weaving, or riveting. A layer of electrical insulation 92 maybe placed over the soldered connection in case the bus bar or connectedpower wire fails at the edge of the solder joint with repeated flexing.The insulation may be tubular in order to surround the wires andconnection. The insulation prevents the broken wire end from contactingthe heating element, causing a short and localized melting of theheating element.

In embodiments that do not include a laminated or otherwisedimensionally stabilized fabric heating element 10, sewing the bus bars62, 64 to the heating element 10 can be difficult. For example, thefabric heating element 10 may stretch or shift on the bias duringsewing. Because of this, some embodiments include bonding a ribbon, orstrip of woven or non-woven fabric, such as a strip about 0.5-2.0 incheswide, or other dimensionally stabilizing woven fabric, film, or fiberreinforced plastic film, to the fabric heating element 10 where the busbars 62, 64 are to be attached. The strip may be bound to the heatingelement 10 along ends 12, 14 using an adhesive, for example. Thesestrips of less stretchable or non-stretchable fabric or film providedimensional stability to the heating element material and preventstretching during the attachment of the bus bars 62, 64. In certainembodiments where the bus bars 62, 64 are located at or near the edgesof the fabric heating element 10, the dimensionally stabilizing ribbonsor strips are bonded to the heating element 10 at or near its ends 12,14. In embodiments where electrically conductive stitching is used toelectrically couple the bus bar 62, 64 and the heating element 10, thestabilizing material may be electrically insulating and serve the dualpurpose of stabilizing the heating element 10 during assembly and actingas an electrically insulating member 72, 74 between the bus bar 62, 64and the heating element 10.

A uniform Watt density output across the surfaces of some embodiments ofthe heating element 10 translates into generally uniform heating of thesurfaces, but not necessarily a uniform temperature. At locations of aheating element 10 that are in conductive contact with a mass acting asa heat sink, for example a body, the heat is efficiently drawn away fromthe heating element and into the body. At those locations where aheating element 10 does not come into conductive contact with the body,for example the peripheral portions, an insulating air gap existsbetween the body and those portions, so that the heat is not drawn offthose portions as rapidly. Therefore, those portions of the heatingelement 10 not in conductive contact with the body will rise intemperature, since heat is not transferred as efficiently from thesenon-contacting portions as from those in conductive contact with thebody. The non-contacting portions of the heating element will reach ahigher equilibrium temperature than that of the contacting portions ofthe heating element. This new equilibrium temperature will be reachedwhen the radiant and convective heat losses equal the constant heatproduction of the heating element. Under the laws of thermodynamics itcan be understood that as long as there is uniform heat production, evenat the higher temperature, the radiant and convective heat transfer fromnon-contact areas of an underbody support of this construction willresult in an equivalent or lower heat flux to the skin than theconductive heat flux at the contacting portions operating at the lowertemperature. Even though the temperature at non-contacting portions ishigher, the Watt density is uniform and, since the radiant andconvective heat transfer is less efficient than conductive heattransfer, the non-contacting portions have an equivalent or lower heatflux to the skin. Therefore, by controlling the contacting portions ofthe heated underbody support to maintain a safe temperature, forexample, via a temperature sensor proximate the heating element 10 in alocation where the element will be in conductive contact with the body,the non-contacting portions, for example the lateral portions, will alsobe operating at a safe (although higher) temperature because of the lessefficient radiant and convective heat transfer. The higher temperaturesin the non-contacting portions also result in more effective radiant andconvective heat transfer compared to a lower temperature. According tosome embodiments, the heating element 10 comprises a conductive fabrichaving a relatively small thermal mass such that when a portion of theheating element 10 that is operating at a first higher temperature istouched, suddenly converting a non-contacting portion into a contactingportion, that portion will cool almost instantly to a second loweroperating temperature.

Various embodiments include heated mattresses, mattress overlays, andpads that automatically optimize both the safety and efficacy of thewarming in multiple zones across the surface of the mattress, mattressoverlay, or pad. The zones are differentiated by whether the mattress ormattress overlay is directly contacting the patient or is substantiallynot contacting the patient. In general, the central portion of themattress or mattress overlay will be contacting the patient and thelateral edge portions will predominately not be contacting the patient.Therefore, the central region will transfer heat to the patientconductively and the lateral regions will transfer heat to the patientvia radiation and natural convection. The location of the centralcontact zone is predictable because the patient is anesthetized andtherefore, is not spontaneously moving or rolling in bed.

FIG. 5 is an aerial view of a heater assembly 1 for use in a heatedunderbody support according to some embodiments. As shown in FIG. 5, theheating element 10 may have a substantially uniform Watt density acrossits surface. This may be accomplished with a conductive fabric heatermaterial. The central zone and the adjacent peripheral zones of theheating element 10 are powered by the same controller. The temperaturesensor assembly 110 which inputs to the controller is attached to theheating element 10 in a location which is predicted to be in directconductive contact with the patient's body when the patient ispositioned on the support—the central zone. Once the patient is inposition on the support, the area of contact between the patient definesa contact portion while the remaining area is the non-contact portion ofthe support. The central zone is therefore the portion of the heatingelement upon which a patient is positioned during normal use and is anestimate of where at least the contact portion is most likely to be.Locating the temperature sensor assembly in the central zone can be usedto optimize the safety and efficacy of the warming mattress or mattressoverlay. During use, in the central zone 10 where the temperature sensorassembly 110 is attached to the heating element 10, the top surface ofthe heated underbody support is in contact with the patient foreffective conductive heat transfer. For safety reasons, the temperatureof the heating element 10 in the conductive zone or contact portion maybe controlled to temperatures no greater than between about 38 and about41° C., for example. In the areas of contact between the patient and themattress or mattress overlay, the patient's body can act as a heat sinkand draw heat from the heating element 10. If the temperature sensorassembly 110 in that region senses the temperature of the supportdecreasing, it provides an input to the controller, and the controllerresponds by increasing the electrical power to the entire heatingelement 10. The temperature of the central zone of the heating element10 may eventually reach—but not exceed—the set point. This assuresoptimal heat transfer as well as optimal safety in the contact portionwhich is the conductive heat transfer region.

In the adjacent peripheral zones, where the heated underbody support istypically substantially not contacting the patient, the added electricalpower to the whole heating element 10 results in an increased heatingelement 10 temperature, which may be greater than the set point ordesired temperature as directed by a user. This occurs because there isno heat sink in contact with the heating element 10 to remove the heat.The non-contact portion will be warmer than the contacting portion. Theincreased temperature in the non-contact portion results in moreeffective radiant heat transfer in the non-contact portion than if thisphenomenon had not occurred. However, since radiant heat transfer isless efficient than conductive heat transfer, despite the highertemperature, the radiant heat is still safe.

For example, the central zone is located substantially in the centralarea of the support, extending along the longitudinal midline of thesupport and measuring about 12 inches wide and about 36 inches long. Theperipheral zone is in general, the 4-6 inch wide strip of heater runninglongitudinally along each side edge of the support.

Additionally, the conductive fabric heating elements 10 may have a lowthermal mass. Therefore, if the peripheral portion of the heatedunderbody support that is operating at the higher temperature istouched, suddenly converting a non-contact zone into a contact zone,that part of the heating element 10 quickly cools to the safe operatingtemperature of the conductive central zone. The non-contact peripheralzones 14 of a heated underbody support may momentarily feel warm whencontacted, but will quickly cool to the lower temperature of the contactzone without transferring sufficient thermal energy to injure thepatient. Thermal mass, or heat storing capacity, is commonly defined asthe product of the mass and the specific heat of a material. Materialswith a low specific heat, a low density, or a combination thereof, willexhibit a low thermal mass. For example, a polymer such as polyurethane,with a density of 1100 kg/m³ and a specific heat of 1.7 kiloJoules (kJ)per kilogram-degree Kelvin has a volumetric heat capacity of 1870kJ/m³−° K, and foam can have a heat capacity of 20-200 kJ/m³−° K. A thinlayer of polyurethane film covering a fabric heating element and a foamlayer has significantly lower thermal mass than a water mattress, forexample, given the volumetric heat of water of 4180 kJ/m³−° K. Thethermal mass of a heated underbody support can therefore be reduced byusing components that exhibit a low density and/or specific heat. Inaddition, reducing the thickness, or total volume of materials used inthe shell, for example, will reduce the thermal mass of the heatedunderbody support. Various embodiments may be made with materials with alow thermal mass such as films, fabrics and foams. Some embodiments donot incorporate materials such as thick pieces of metal, liquid water orwater-based materials such as gels that have relatively high thermalmasses.

In these embodiments, when the temperature sensor assembly 110 isattached to an area of the heating element 10 that is typically inconductive contact with the patient during normal use, any other area ofthe heating element 10 that is also in conductive contact with thepatient will also be at or near the set point or desired temperature.The temperature differentiation and location of the zones is automaticand depends on whether or not there is conductive contact between theheating element 10 and the patient.

Various embodiments therefore optimize both heat transfer and safety byautomatically creating multiple zones in the heated underbody support.The non-contact, radiant heat zones which are typically peripheral,operate at a higher temperature than the patient contact, conductiveheat zones which are typically central.

When not stretched, fabric heating elements 10 as described hereinprovide an even heat output or Watt density across their surface, unlessthey are folded or wrinkled which can double or triple the heatingelement 10 layers in the folded or wrinkled portion. The entire heatingelement 10 may have a relatively low Watt density, such as less than 0.5watts per square inch, for example. Therefore, some embodiments preventlocal wrinkling of the heating element 10. An embodiment of a heatedmattress overlay 2 including a heater assembly 1 and a compressiblematerial layer 20 and having reduced wrinkling or folding is shown inFIG. 6. It should be noted, however, that whether a unit is described asa heated mattress, heated mattress overlay, or heated pad is largelyunimportant, and most embodiments could be used variously as heatedunderbody supports. While a heated mattress overlay may have a thinlayer of padding, a heated pad typically has padding that may be thin orthick, a heated mattress may have an even thicker layer of padding. Assuch, various embodiments may be used alone, in the manner of amattress, or on top of a mattress, in the manner of a mattress overlay.Descriptions relating to heated mattress overlays therefore also applyto descriptions of heated mattresses and heated pads, and vice versa.

The mattress overlay 2 as shown in FIG. 6 includes a fabric heatingelement 10 with bus bars 62, 64 attached that is additionally attachedto a layer of compressible material 20 by a layer of adhesive 30 beneaththe heating element 10. To prevent wrinkling, the compressible materiallayer 20 may be comprised of a simple urethane upholstery foam or itsequivalent or one of the many “high tech” foams such as visco-elasticfoams. Many foams are suitable for the compressible material layer 20but should be durable and able to prevent wrinkling of the heater duringuse, yet should also be flexible, stretchable and accommodating. In theembodiment shown, the mattress overlay 2 also includes an upper shell 40and a lower shell 42 forming an outer shell that encases the heaterassembly 1 and compressible material layer.

The compressible material layer 20 may be a single layer of foam or maybe a stack of materials that includes a layer of foam. This stack couldinclude foam layers of different densities, different accommodationproperties, different stiffness or different polymers. Additionally, thecompressible material layer can include other materials such as woven ornon-woven fabrics or films, to achieve other characteristics such aslateral stiffness or durability and strength. The term compressiblematerial layer 20 therefore refers generally to single layers ofcompressible material such as foam as well as multilayered stacks thatmay include one or more layers of foam and may include other materials.Also, the layer of compressible material may alternatively be a layer offoam as described above.

Attachment of the heating element 10 to the compressible material layer20 may be achieved by adhesive bonding across the entire interfacebetween the two. Alternately, the heating element 10 may be bonded tothe compressible material layer 20, intermittently across its surface,for example in dot, matrix, lines, boxes or other patterns or in arandom pattern. The bond may be made with an adhesive comprising apressure-sensitive adhesive without a reinforcing fiber or film carrier.Since the compressible material layer 20 may be flexible, stretchableand compressible, such a bonding made with such an adhesive does notalter the flexibility and stretch-ability of the heating element 10 orheated mattress overlay 2. Alternately, the heating element 10 may beattached to the compressible material layer 20 only along one or more ofthe edges 12, 14, 16, 18 such as along two opposing edges such as edges12, 14, or in an intermittent pattern.

FIG. 7 depicts a cross section of a portion of an alternative embodimentof a heated mattress overlay 2, in which the fabric heating element 10is bonded to an overlaying plastic film layer comprising an upper shell40 by a layer of adhesive 35. In such embodiments, the upper shell 40can be stretched and held in position by the compressible material layer20 or by anchoring the mattress overlay 2 laterally, with or withoutbonding the shell 40 to the heating element. When the stretched layer ofupper shell material is bonded to the heating element 10, this mayreduce or prevent wrinkling or folding of the heater element 10 and yetmaintain flexibility and stretchability (depending on the stretchabilityof the shell material). In the embodiment shown, the heated mattressoverlay 2 further includes a lower shell 42 beneath the compressiblematerial layer 20.

An alternative embodiment is shown in the heated mattress overlay 2 ofFIG. 9, a cross section of which is shown in FIG. 8. In this embodiment,the fabric heating element 10 is anchored to a shell including an uppershell 40 and a lower shell 42 along its edges 12, 14, 16, 18 and thusheld in an extended and wrinkle-free condition. Anchoring strips 46comprised of plastic film or a suitable alternative are attached alongthe edges 12, 14, 16, 18 of the heating element 10, such as by sewing toform a sewn connection 85, though other forms of attachment may be usedsuch as adhesive bonding. The anchoring strips 46 may extend along allfour edges 12, 14, 16, 18 of the heating element 10 to form a peripheralbond 48. Alternatively, the anchoring strips 46 may extend along onlyone pair of opposing edges such as edges 12 and 14 or edges 16 and 18.The anchoring strips 46 may be made of the same material as the shells40, 42, such as plastic film, and therefore can be bonded around theperiphery of the mattress overlay 2, being sandwiched between andincorporated into the bond between the upper shell 40 and lower shell42.

Since some embodiments maintain the heating element 10 in an extendedand unwrinkled condition in order to avoid hot spots, more than one ofthese heating element 10 anchoring embodiments may be usedsimultaneously. To maintain flexibility, conformability andstretchability, the upper and/or lower shell 42, 44 may be adhered tothe heating element 10 or the compressible material layer 20, acrosstheir broad surfaces as shown, for example, in FIG. 7, or may not be soadhered. However, in an alternate embodiment the heating element 10 canbe bonded to the upper shell 40, for example. This may be advantageousfor minimizing wrinkling of the heating element 10 or plastic film layerof the shell 40, 42.

Stretching the heating element 10 from the edges 12, 14 could result inhammocking of the heating element 10, such as if the mattress overlay 2or pad is anchored tightly to the operating room table along the lateraledges. Various embodiments therefore include a beveled edge 24 on thecompressible material layer 20, as shown in FIG. 10, for example, tohelp prevent hammocking by creating a slight excess of heating element10 material as the heating element 10 transitions across the anglebetween the upper surface 21 of the compressible material layer 20 andthe beveled edges 22,24. Additionally, the angle also creates an area ofcompressible foam that can compress in response to the heating element10 being deformed by a weight resulting in the heating element 10pulling toward the center from the edges 12, 14. Rather than beingstretched tight out to the edge as would occur with a non-beveledcompressible material layer 20, thereby potentially forming a hammock,the heating element 10 moves toward the center by compressing thecompressible material layer 20 at the angle between the upper surface 21and the beveled edge 24 of the compressible material layer 20, inresponse to deformation by a weight applied to the central area of theheated mattress or mattress overlay 2. In this way, the risk ofhammocking is further reduced or eliminated.

The compressible material layer 20 (or layer of compressible material)supporting the heater assembly 1 in certain embodiments could be almostany thickness that is advantageous for the given application (forexample, 0.5-6.0 inches). The compressible material layer 20 may beuniform in thickness and density or it may be contoured in thickness,shaped, scored or segmented according to areas of different densities.

FIG. 10 depicts a cross section of a heated mattress overlay 2 includinga shaped compressible material layer 20 according to variousembodiments. In this embodiment, the compressible material layer 20 isbeveled or tapered along one or more edges, such as the edges that abutand support the bus bars 62, 64 which are attached to the compressiblematerial layer 20 along the beveled edges 22, 24. The compressiblematerial layer 20 is generally planar with an upper surface 21 and anopposing and parallel lower surface 23. The beveled ends 22, 24 of thecompressible material layer 20 are not perpendicular to the surfaces 21,23 but rather angle inwardly, toward the upper surface 21. On crosssection, the compressible material layer 20 is trapezoidal in shaperather than rectangular, with the lower surface 23 forming the largertrapezoid base and the upper surface 21 forming the smaller trapezoidtop. Alternatively, the lower portion of the edge could be perpendicularto the bottom surface while only the upper portion of the edge may beangled inwardly to form a bevel. Other embodiments including bevelededges are also anticipated.

The portions of the heating element 10 attached to the bus bars 62, 64may be bonded to the compressible material layer 20 along the beveledends 22, 24. Locating the bus bars 62, 64 on the beveled ends 22, 24 ofthe compressible material layer 20 provides some protection of the busbars 62, 64 from mechanical stress when patients are sitting or lying onthe underbody support. Alternatively, to provide additional protectionto the bus bars 62, 64, the heating element 10 may be wrapped around thecompressible material layer 20 and onto the bottom surface 23 so thatthe bus bars 62, 64 are located under the compressible material layerbeveled ends 22, 24 and attached to the bottom surface 23 as shown inthe cross section shown in FIG. 11, for example. In a furtheralternative shown in FIG. 12, the beveled piece of foam that is removedfrom the compressible material layer 20 or any other triangular or wedgeshaped piece of foam of complementary size and shape to fit the spacemay be bonded over the heater assembly's bus bars 62, 64, along thebeveled edges 22, 24 of the compressible material layer 20 to form afiller 25, to fill in the beveled space and protect the bus bars 62, 64.The foam filler 25 may be sized such that, when in place above the busbars, the horizontal upper surface of the heated mattress overlay 2 (orother underbody support) above the central, non-beveled portion of thefoam, is level with the horizontal upper surface of the overlay 2 abovethe beveled end 24. In these embodiments the heating element 10 extendsacross the upper surface 21 of the compressible material layer 20, andthe bus bars 62, 64 are away from and lower than the upper surface 21.In this way, the bus bars 62, 64 may be physically protected from damageby bonding them onto or beneath the beveled edges 22, 24 of thecompressible material layer 20, where they are effectively recessed fromthe upper surface 21 of the compressible material layer 20. The bevelededges 22, 24 of the compressible material layer 20 allow the bus bars62, 64 to be optionally covered with a foam filler 25 to act as aprotective barrier in this location for added protection, withoutadversely affecting the look of the smooth top surface of the underbodysupport, thereby basically filling the bevel space with a foam filler 25to create an overall rectangular cross sectional shape.

In other embodiments, a portion of the compressible material layer 20 isthinned or scored in an area, from one lateral edge to the other of thearea, with the area located to overlie the area of transition from onecushion of an operating table to the adjacent cushion under normalconditions of use. The thinning or scoring may be on the bottom surface23 of the compressible material layer 20 and therefore away from thepatient contact top surface 21. Since operating room tables are designedto flex at the area between the operating table cushions, a thinnedcompressible material layer 20 at the area of transition betweencushions will aid in flexion of the heating element 10 and reduce thechances of the heating element 10 wrinkling during flexion.Alternatively, the compressible material layer 20 could be scored or cutor otherwise have one or more gaps or channels completely through orpartially through its thickness on the bottom surface 23 at the flexionlocations or other areas where added flexibility is important, as shownin FIG. 13, for example. In the embodiment shown, multiple smallchannels 27 are present in a portion of the compressible material layer20 where the compressible material layer 20 is thinner. These channels27 may extend across the compressible material layer 20, from one end tothe opposing end, such as across the width or the length of thecompressible material layer 20, such as in a direction parallel to andaligned with the transition between operating table cushions. In use,the underbody support may be positioned over a table or bed with whichit is designed to be used such that the channels are located over theflexion locations of the table or bed. The table or bed may then beadjusted by bending at a flexion point (such as to raise or lower apatient's upper body or legs by bending or extending the patient at hisor her hips) and the compressible material layer 20 of the underbodysupport can bend easily at this location due to thinness or scoring atthe location of flexion, while the heating element 10 can likewise bendwithout wrinkling or folding due to its flexibility and elasticity.

In some embodiments, the compressible material layer 20 may be thinnedor scored or have gaps or channels longitudinally in order to increaseflexibility for bending the heated underbody support around alongitudinal axis such as a long axis of a body. This may beadvantageous to aid in wrapping the heated underbody support around apatient being in the lateral position while laying within a “bean bag”or “peg board” positioner. The longitudinal thinning or scoring orpresence of gaps or channels allows the heated underbody support to bewrapped around the dependent portion of the patient, increasing the areaof surface contact between the heating element 10 and the skin whileavoiding wrinkling of the heating element 10 due to the bending of thecompressible material layer 20. In these embodiments, the bending of thecompressible material layer 20 can be facilitated by corrugations in thelower shell 42, which may be created by , at a location corresponding toor adjacent to the location of the gaps or channels in the compressiblematerial layer 20. The corrugations of the shell material may belongitudinal or from side to side. The excess lower shell materialcreated by the corrugations may allow the support to be bent forward atthe edges or ends, without causing the upper shell 40 and heatingelement 10 to wrinkle The redundant lower shell material 42 of thecorrugations, in conjunction with gaps or channels in the compressiblematerial layer 20, allow the lower shell to stretch when the support isbent forward, rather than the upper shell 40 and heater element 10compressing and wrinkling

In some embodiments, the compressible material layer 20 is segmentedinto portions having different thicknesses or different materialcomposition or characteristics. For example, the compressible materiallayer 20 may include a central portion that may be a rectangular, roundor oval section portion within a surrounding portion. Other sectionalshapes are anticipated. The surrounding portion may resemble a pictureframe or may only surround a portion of the central portion. The centralsection or sections may be filled with a plug of less dense foam, forexample, to increase the accommodation of lightweight pediatric patientsor patients' extremities. The surrounding portion of the compressiblematerial layer 20 which may surround the plug may be a denser foam thatis more suitable for stabilizing the heating element 10, for example toprevent wrinkling of the heating element 10. An example of such anembodiment is shown in FIG. 14, which is an aerial view of a heatedmattress overlay 2 with a compressible material layer 20 with acentrally located plug 27 of less dense foam.

In still other embodiments, such as the heated mattress overlay 2embodiment shown in the cross section in FIG. 15 or other heatedunderbody supports, the compressible material layer 20 includes adepression 29 in a given location to encourage the proper location ofthe patient on the mattress overlay 2 by contouring the compressiblematerial layer 20, for example. The depression 29 may also stabilizesmall pediatric patients on the mattress overlay 2. The depression 29may be a longitudinal, semicircular half-pipe shape gap or cut out thatcreates a trough-like depression for the pediatric patient to lay in. Adepression 29 in the compressible material layer 20 for small pediatricpatients may also increase the amount of skin surface in contact withthe heating element 10 by extending the heating element 10 up the sidesof the patient's body. The increased surface area of the supportcontacting the sides of the pediatric patient increases the heattransfer between the support and the patient. The depression 29 alsoassures accurate positioning so that the patient is contacting thetemperature sensor assembly 110 if it is located substantially in themiddle or at or near the bottom of the depression 29. For all of thesereasons, a pediatric heated mattress or mattress overlay 2 with alongitudinal depression 29 cut into the compressible material layer 20,may be more effective at warming pediatric patients than a simple flatunderbody support. Such heated underbody supports may also be moreeffective for heating adult patients. Other examples of contouring,shaping or segmenting the compressible material layer 20 areanticipated.

In some embodiments, the temperature sensor assembly 110 includes asubstrate, for example, of polyimide (Kapton), on which the temperaturesensor, for example, a surface mount chip thermistor (such as aPanasonic ERT-J1VG103FA: 10K, 1% chip thermistor), is mounted. A heatspreader, for example, a copper or aluminum foil, is mounted to anopposite side of the substrate, for example, being bonded with apressure-sensitive adhesive. The substrate is relatively thin, forexample about 0.0005 inch thick, so that heat transfer between the heatspreader and sensor 110 is not significantly impeded. The temperaturesensor assembly 110 may be bonded to the fabric heating element 10 withan adhesive layer, for example, hotmelt ethyl vinyl acetate. Thetemperature sensor assembly 110 may be potted with a flexibleelectrically insulating material, such as silicon or polyurethane. Aheat spreader is a desirable component of a temperature sensor assembly110, according to some embodiments, since conductive fabrics employed bythe heating element 10, such as those previously described, may notexhibit perfectly uniform resistance across surface areas thereof. Insome embodiments, a secondary over-temperature sensor assembly 115 ofsimilar construction to the temperature sensor assembly 110 may belocated within one inch of the primary control sensor, so that both thetemperature sensor assembly 110 and the secondary over-temperaturesensor assembly 115 may respond to the same inputs. In some embodiments,both assemblies 110, 115 are mounted to the same heat spreader.

In embodiments where the temperature sensor assembly 110 and secondaryover-temperature temperature sensor assembly 115 are attached to theheating element 10 and the heating element 10 is separated from theenvironment by an upper film 40, there is a risk that the assemblies110, 115 may be influenced by environmental factors. Under certainconditions, the sensors may measure the “cool” ambient temperature fromthe environment, or from an object such as a wet towel or a metal paninadvertently positioned over the temperature sensor 115, and providethat input to the controller which will then drive the heating element10 into an over-temperature condition in areas contacting the patient.Various embodiments of the heated underbody supports may reduce oreliminate this risk as described below.

FIG. 16 is an aerial view of a heated mattress overlay 2 in which a thinlayer (such as less than about 0.5 inches) of compressible material suchas foam is located around the temperature sensor assembly 110 and theover-temperature sensors assembly 115 to limit the effect ofenvironmental or ambient temperatures in instances where the patient isnot properly positioned over the temperature sensor assembly 110.Alternatively, a thin layer of compressible material such as foam maycover some or all of the upper surface of the heater assembly 1. In somealternative embodiments, the material layer may be in the form of a ring120 surrounding the temperature sensor assembly 110, as shown in FIG.17. When the patient is not positioned over the temperature sensorassembly 110 and over temperature sensor assembly 115, the ring 120 willremain expanded (uncompressed) and lift the upper shell 40 away from thetemperature sensor assembly 110 and the over temperature sensor assembly115, creating an air space 122 within the ring of foam 120 and betweenthe temperature sensor assembly 110 and the upper shell 40. In thisinstance, the air space 122 will act as a thermal insulator, minimizingthe influence of the environmental temperature on the temperature sensorassembly 110 and the over temperature sensor assembly 115. The spacewithin the ring 120 should be large enough (for example about 0.5 toabout 2.0 inches) and the ring material should be compressible enough toallow the over-laying layer of plastic film of the upper shell 40 to becompressed directly against the temperature sensor assembly 110 and theover temperature sensor assembly 115 when a patient is laying on theassemblies 110, 115, as shown in the cross-sectional view of FIG. 18, inwhich the downward force of the patient (not shown) is indicated bydownward printing arrows. In this condition, the temperature sensorassembly 110 and the over temperature sensor assembly 115 will respondto the temperature of the heating element 10 that is in direct thermalcontact with the patient. This affords the correct information to thecontroller to allow for accurate temperature control of the heatedunderbody support. The weight of the patient laying on the ring 120surrounding the assemblies 110, 115 or on a material layer over theassemblies 110, 115 will compress the material and the patient will endup in thermal contact with the temperature sensor assembly 110 and theover-temperature sensor assembly 115. If the patient is not positionedover the temperature sensor assembly 110 and the over-temperature sensorassembly 115, the non-compressed ring 120 or layer will thermallyinsulate the assemblies 110, 115 from the cool environmentaltemperatures which could otherwise cause the heating element temperatureto rise to an over-temperature condition.

To prevent overheating, certain embodiments include one or moretemperature sensor assemblies 110 in the heated underbody support thatcan sense the temperature in a desired area and then provide feedback toa controller. The temperature sensor assembly 110 can be placed in anarea that would be in contact with a patient as described above or in anarea that would reflect an average temperature of the heated underbodysupport. The controller may shut off the power supply to the heatingelement and/or triggers an alarm, such as an audible or visible alarm,if the sensed temperature is too high, such as if the temperature is ator above a maximum or threshold temperature. Thus, the temperaturesensor assembly 110 therefore acts as a safety feature to help protectpatients from overheating.

Yet other embodiments include additional safety features in case thetemperature sensor assembly 110 does not reliably report an accurateaverage temperature of the heated underbody support. This could happenin a number of situations. In some cases, the temperature sensorassembly 110 itself may simply be damaged and may provide falseinformation to the controller. In other cases, the temperature sensedmay be cooler than the temperatures of other areas of the heatedunderbody support. This could occur, for example, if a “thermalgrounding” condition should occur, for example if a cool object such asa metal pan or a bag of IV fluids were placed on the temperature sensorassembly 110. The cool object could act as a heat sink and absorb heatfrom the heated underbody support, causing the area around the assembly110 to feel cooler. In another example, the area of the heated underbodysupport near the temperature sensor assembly 110 may become wet ordamaged. In each of these examples, the temperature of the heatedunderbody support in the temperature sensor assembly 110 area may becooler than the temperature of other areas of the heated underbodysupport. Alternately, if the portion of the heating element 10 incontact with the temperature sensor assembly 110 fails, the assembly 110may not detect that the heating element 10 is being adequately energizedand may cause the controller to supply more power to the heating element10. Finally, the temperature sensor assembly 110 itself could fail. Anyof these fault conditions could result in significant over-temperatures(temperatures above a desired temperature) of the heating element 10when the inaccurately cool sensed temperature results in the controllercontinuing to supply power to the heating element 10, even though thetemperatures in some or all areas are too high. If undetected, thetemperature would continue rising to excessive levels and body parts incontact with these areas of the heated underbody support may sufferthermal burn injury if in contact with the heated underbody support fora prolonged period of time. To prevent this, various embodiments includesafety features which allow the controller to detect these faultconditions and then turn off and/or signal an alarm, as describedfurther below. The additional safety feature may be somewhat or entirelyindependent of the temperature sensor assemblies 110, 115. Thisindependence can provide an additional safety feature that can detect orprevent injury in the event of a failure or inaccurate reading of thetemperature sensor assemblies 110, 115.

For example, some embodiments provide a safety feature that cuts powerto a heater assembly 1 after a certain period of time has elapsed (a cutoff time), irrespective of the feedback provided by a temperature sensor110 concerning the heated underbody support temperature. That period oftime may be longer than it takes for the mattress or mattress overlay 2to reach its threshold or desired or maximum cut-off temperature undernormal operating conditions, but shorter than it normally takes to causethermal burn injury and may be determined by the manufacturer and setinto the controller. This safety feature, referred to as a shut-offtimer, may be controlled by the controller as described below, forexample.

The operation of some embodiments of the heated underbody supportsystems will now be described. In operation, the controller is firstturned on or activated, prompting the power source to begin supplyingpower to the heating element 10. The heating element 10 continues toreceive this power until the temperature sensor assembly 110 senses athreshold or desired temperature. Any type of duty cycle and voltagelevel can be used, so long as a desired threshold temperature isachieved in a reasonable amount of time. The threshold temperature canbe any desired temperature that medical personnel wish to supply to apatient. In some embodiments, the threshold temperature is 37° C., 39°C., 41° C., or other temperatures and may be preset or may be set by auser. Some patients (e.g., those with poor blood perfusion) should nothave prolonged contact with conductive heat in excess of approximately39° C. Thus, according to certain embodiments, the threshold temperatureis set by the user to a maximum of approximately 40° C. in order toachieve a temperature of about 39-40° C. on a surface of the heatedunderbody support. The skin temperature may or may not reach thisthreshold temperature of the heated underbody support. In many cases,the skin temperature is slightly lower than the threshold temperature.

Once the temperature sensor assembly 110 senses the thresholdtemperature, the controller prompts the power source to stop supplyingpower to the heating element 10. At some point after the power supply isstopped, the temperature of the heated mattress or mattress overlay 2cools to below the threshold temperature. Once the temperature sensorassembly 110 senses a temperature below the threshold temperature, thecontroller prompts the power source to again supply power to the heatingelement 10. This process operates much like common thermostats andcontinues to oscillate on and off around the threshold temperature untilthe controller is shut off by the user.

In embodiments including a shut-off timer, the shut-off timer operatessimultaneously during the process just described. Regardless of thetemperature sensed by the temperature sensor assembly 110, the shut-offtimer limits the amount of time that power is supplied to heatingelement 10. This way, in case the temperature sensor assembly 110 neverreaches the threshold temperature (even though other areas of the heatedunderbody support may be above the threshold temperature), the shut-offtimer only allows the power to be supplied for a limited time. Theshut-off timer responds to an indication that the prescribed thresholdtemperature has been reached in less than the prescribed shut-off timertime limit. The indicators of reaching the threshold temperature can bea direct temperature reading from the temperature sensor assembly 110 orthe controller or detection of at least a momentary interruption ofpower to the heating element 10. If the timer function does not detectan indicator of the threshold temperature having been reached within theprescribed time, the controller will discontinue power to the heatingelement 10 and/or signal an alarm. This is an additional safety featurethat helps to prevent patients from being exposed to temperatures at orabove the threshold temperatures for a prolonged period of time.

According to some embodiments, once the controller is turned on, itprompts the shut-off timer to start. The shut-off timer runs for adesired period of time and upon expiration of this period of time, thecontroller prompts the power source to stop supplying power to theheating element 10. In addition, the controller may signal an audibleand/or visible alarm and/or display a visible cue to let the user, suchas medical personnel, know that the desired time period has expired. Theexpiration of the time period tells the user that the temperature sensorassembly may not be working, the heating element in the area of thetemperature sensor may be damaged, or the resistance of the heatingelement may have increased to the point where the resulting Watt densityis too low to allow the heating element to reach the thresholdtemperature within the time period, or the temperature sensor may beexperiencing thermal grounding, for example. Any of these conditionsconstitute failure modes. None of these failure conditions could havebeen detected by the control temperature sensor.

If the temperature sensor assembly 110 is functioning properly, the timeperiod for power supply allowed by the shut-off timer should not run outbefore the threshold temperature has been reached and therefore wouldhave no effect on the power. Each time the temperature sensor assembly110 reaches the threshold temperature, the controller prompts the powersource to stop supplying power and also stops and resets the shut-offtimer. Once the sensed temperature cools to less than the thresholdtemperature, the controller prompts the power source to again supplypower and also starts the shut-off timer. This process continuesthroughout normal operation of the heated underbody support. Should thetemperature sensor assembly 110 ever malfunction and fail to sense athreshold temperature within the shut-off timer time period or if theshut-off timer fails to detect at least a momentary discontinuation ofpower to the heater indicating that the threshold temperature has beenreached, the controller will prompt the power source to stop supplyingpower and/or may trigger an alarm. The user would then fix the offendingcondition, e.g., by removing a metal pan or other object that may beinfluencing the temperature sensor, or by disposing of the heatedunderbody support and replacing it with a new one. Thus, embodiments ofthe heated underbody support may have an additional safety feature toprotect patients.

The period of time selected for the shut-off timer is a time period thatis less than a time it takes for thermal burn injury to occur with aparticular heated underbody support (“thermal burn injury time”). Thethermal burn injury time may vary depending on the type of mattress, theWatt density of the mattress and/or the type of power supplied to suchmattress. The shut-off timer may be preset by the manufacturer to asingle time or to a time that varies depending upon the thresholdtemperature, or may be set by the user.

Accordingly, the time limit imposed by the shut-off timer may be thesame regardless of whether the heating element 10 is just beginningoperation or is in the middle of operation. In other embodiments, thecontroller may make a determination that the heating element 10 has beenoperating for a period of time at a steady state (e.g., as evidenced bycontinued cycling of the power supply over a period of time) and mayadjust the shut off time lower than its setting for initial start uptime.

The shut-off time period may depend upon the Watt density of the heatedunderbody support. For heated underbody supports operating at a Wattdensity of less than approximately 0.25 watts/square inch, programmingthe timer for a shut-off time period of about 20 minutes may bedesirable. To provide an additional margin of safety, programming thetimer for a shut-off time period between about 5 and about 15 minutesmay be desirable. This time period is well below the predicted thermalburn injury time, regardless of whether the heated underbody support isjust beginning operation or is in the middle of operation. Thus, incertain embodiments, the shut-off timer is set to expire after a timeperiod which is between about 5 and about 15 minutes. In someembodiments, the shut-off timer is set for a shut-off period of about 10minutes. The time period may need a minimum of about 5 minutes in theseembodiments because it could take up to 5 minutes for a room temperatureheating element 10 to reach the threshold temperature. The time periodmay be greater than what is required to reach the threshold or desiredtemperature under normal operating conditions in order to avoid being anuisance to the user of the heated underbody support.

Heated underbody supports having a Watt density higher than 0.25watts/square inch might have a shut-off time period that is shorter,perhaps about 10 minutes or less. Supports operating at a higher Wattdensity (e.g., 0.5 watts/square inch) may have even shorter shut-offtimes. In contrast, heated underbody supports having a Watt density muchlower than 0.25 watts/square inch might have a time period that islonger, perhaps more than about 10 minutes, as discussed above.

The operation of the heated underbody support may be described withreference to a temperature sensor assembly 110 having a singletemperature sensor. Of course, temperature sensor assemblies 110 can beused that have multiple temperature sensors. For example, thetemperature sensors can be provided in the form of conventionaltemperature sensors, over-temperature sensors, and super-overtemperature sensors, as described in U.S. application Ser. No.11/537,189, the contents of which are incorporated herein by reference.Each temperature sensor can provide input to the controller. Thetemperature sensors can all have the same threshold temperature or somecan have different threshold temperatures. For example, sensors locatedin an outer or peripheral area 116 of the heating element 10 that wouldnot normally be in contact with a patient may have a higher thresholdtemperature than sensors located in an area that would normally be incontact with a patient during normal use.

In embodiments having multiple temperature sensors, the controller canbe configured in any manner so that when a specific temperature scenariois reached, it prompts the power source to stop the supply of power andresets the shut-off timer. For example, in one embodiment, the thresholdtemperature can be the same for each sensor, and the controller systemcan determine an average of the overall sensed temperature. When adesired average temperature is reached, the controller can shut offpower and the shut-off timer can be reset. In other embodiments, thecontroller can be configured to shut off power and the shut-off timercan be reset each time a threshold temperature for any sensor isreached. Varieties of scenarios are possible and are within the scope ofthis disclosure. In any event, no matter how many sensors are providedand no matter what the threshold temperatures are, the shut-off timercan operate the same way. The shut-off timer begins to track time whenthe controller is turned on and continues until either the shut-off timeperiod expires or until the controller resets the shut-off timer or itsenses an interruption of power to the heating element 10 when aprogrammed temperature threshold is reached.

A flow chart depicting the operation or programming of a controlleraccording to various embodiments is shown in FIG. 19. At step 300, thecontroller is activated to supply power to the heating element 10. Thisimmediately starts the timer at step 305 and also starts receivingmeasured temperatures from temperature sensors at step 310. At step 315,the controller determines whether the measured temperature is less thanthe set point or threshold temperature. If the answer at step 315 is NO,the controller prompts the power source to shut off the power supply atstep 320. This in turn stops and resets the timer at step 325. The timerdelays at step 330 and then repeats this process starting at step 305.If the answer at step 315 is YES, the controller prompts the powersupply to turn the heat on if it is not already on at step 335. Thecontroller then determines whether the timer has reached the maximumtime period at step 340. If the answer in step 340 is YES, thecontroller shuts off the power and/or signals an alarm at step 345. Ifthe answer in step 340 is NO, the controller delays at step 350 andrepeats this process starting at step 310.

In many of the embodiments described above, the shut-off timer iscorrelated to a threshold temperature in an on/off power control system.That is, the controller resets the timer and stops a supply of powereach time the threshold temperature is sensed. However, the shut-offtimer can be correlated to operating parameters other than thetemperature sensor measurement. In addition, the controller may be moresophisticated than an on/off power supply system. For instance, in someembodiments, the controller modulates the amount of power supplied(rather than simply turning a single power type on and off). Here, thecontroller monitors temperature of the heated underbody support based oninput received from one or more temperature sensors and modulates thepower levels accordingly. For example, as the sensed temperatureapproaches a threshold temperature, the controller can gradually orincrementally reduce the power level. As the sensed temperature fallsbelow the threshold temperature, the controller can increase the powerlevel to increase the temperature. If the sensed temperature is farbelow a threshold temperature, the controller can increase the powerlevel even higher than that for a temperature just below the thresholdtemperature.

Under a modulated power control system, the controller and shut-offtimer can be programmed so that if the power level does not fall below athreshold level within a desired period of time, the timer expires andthe controller shuts off the power supply and/or signals an alarm.Likewise, each time the power level does fall below the threshold level,the timer is reset. Accordingly, in such embodiments, the shut-off timerreset may be based on the power supply level and not directly ontemperature or power supply interruption.

One known power modulating controller which may be used in someembodiments is a PID (proportional/integral/derivative) based controlsystem. In embodiments including a PID control system, the controllercan monitor one or more process control parameters, such as an integralcontrol term. The controller and timer can be programmed so that if theintegral control term does not reach a desired level within a desiredperiod of time, the shut-off timer time limit expires and the controllershuts off the power supply. Likewise, each time the integral controlterm reaches the desired level, the timer is reset.

In some embodiments, the temperature control comprises a thermostaticswitch, such as a bi-metallic thermostat, thermally coupled to theheating element 10 and in-line with the power supply for the heatingelement 10. In such embodiments, the switch opens, thereby cutting offcurrent to the heating element 10 when the heating element 10 and itsthermally coupled switch reach a set point temperature. The shut-offtimer can sense the discontinuation of power to the heater and reset itstimer.

In some embodiments, the flexible heating element 10 itself may comprisea temperature sensor. In such embodiments, the flexible heating element10 is formed of a material having a resistance that varies withtemperature. The controller may determine the temperature of theflexible heating element by measuring the resistance or change inresistance in the power supply circuit. The resistance of the heatingelement 10 may also be used to determine the Watt density output of theheating element 10. Thus, the heating element resistance measurement maybe used as a control parameter by the controller to control or adjustthe Watt density output of the heated underbody support as desired.

The shut-off timer may comprise a safety device that may operateindependently of the temperature measured by the temperature sensor andcontrol circuit, based on the assumption that the heating element 10will normally reach operating temperature in less than a prescribedamount of time, for example, ten minutes. Normally, the electric currentto the heating element 10 may be on continuously until the thresholdtemperature is reached. Then the controller maintains the desired settemperature by either turning the current on and off or the controllerproportionally reduces and increases the current flow. If the shut-offtimer does not sense that the current has been at least momentarilyturned off or reduced prior to the shut-off time elapsing, or does notsense that a prescribed temperature has been reached, the controllerwill recognize this as a fault condition.

In some embodiments, such as the embodiment as shown in FIG. 20, theremay be an upper insulating layer 125 which may be made of foam or highloft fibrous material, for example, between the heating element 10 andthe upper shell 40. If the material of the upper insulating layer 125 iseasily compressible, it may extend in a thin layer (for example about0.25 inches or less, such as about 0.01 to about 0.025 inches) over theentire surface of the heating element 10 with minimal detrimental effecton heat transfer. This upper insulating layer 125 may reduce the impactof environmental temperature on the temperature sensor assembly 110 ininstances where a patient is not positioned on the temperature sensor110. To improve heat transfer and retain a thin, distributed insulatinglayer over the heating element 10, an array of holes 127 (for example0.5-2.0 inches in diameter) can extend through the upper insulatinglayer 125 as shown in FIG. 21, for example. Hole shapes other than roundmay also be used. The holes 127 may spread over the entire layer 125 oronly a portion of layer 125. When the upper insulating layer 125 iscompressed by the weight of the patient, the upper shell 40 of theheated mattress or mattress overlay 2 directly contacts the heatingelement 10 within each of the holes 127. The holes 127 may be absent(the material may be continuous and uninterrupted) in certain locationssuch as along the edges of the upper insulating layer 125 above the busbars 62, 64 where the uncompromised material may provide addedprotection to the bus bars 62, 64. This construction gives improved heattransfer by placing the heating element 10 very close to the patientwhile still protecting the heating element 10 and temperature sensorassemblies 110 from unwanted environmental thermal influences.

The combination of conductive fabric heating elements 10 made fromflexible and stretchable material, bus bars 62, 64 attached nearopposing edges 12, 14 of the heating element 10, one or more temperaturesensors 110 and a controller, comprises a heater assembly 1 according tosome embodiments. The heater assembly 1 may be secured to a compressiblematerial layer 20 or other compressible layer and may be covered with awater-resistant shell 40, 42 that may be made of a stretchable plasticfilm such as urethane or PVC, however, other film materials andfiber-reinforced films are anticipated.

The shell 40, 42 protects and isolates the heater assembly 1 from anexternal environment of the heater assembly 1 or heated underbodysupport and may further protect a patient disposed on the heatedunderbody support from electrical shock hazards. According to someembodiments, the shell 40, 42 is waterproof to prevent fluids, forexample, bodily fluids, IV fluids, or cleaning fluids, from contactingthe heater assembly 1, and may further include an anti-microbialelement, such as SILVERion™ antimicrobial available from DomesticFabrics Corporation (Kinston, N.C.), which is extruded in the plasticfilm of the shell material.

In some embodiments, a layer of plastic film is placed over each broadsurface of the heater assembly 1, as an upper shell 40 and a lower shell42 but is not bonded to the heater assembly. The two layers of plasticfilm are bonded to each other around the periphery of the heaterassembly 1 to form a water-resistant shell. The bond may be from heat,radio frequency (RF), ultrasound, solvent or adhesive, for example. Theheater assembly 1 may be “free floating” within the shell with noattachment to the shell, or can be attached to the shell, such as onlyat the edges 12, 14, 16, 18 of the heater assembly 1 as described above,for example. This bond construction around the periphery of the heatedunderbody support creates a durable shell without folds, creases,crevasses or sewing needle holes that can collect infectious debris andbe difficult to clean. The heater assembly 1 covered by a shell ofplastic film and optionally including a foam or other compressiblematerial layer comprises a heated mattress, mattress overlay, or padaccording to some embodiments.

In certain embodiments, such as the embodiments shown in FIGS. 22 and23, the shell construction allows the power entry module 130 to belocated and bonded between the shell, such as the layers of plasticfilm, at the edge of the shell within the bonded layers 48. The powerentry module 130 can be bonded with adhesive, solvent, heat, RF orultrasound for example, between the adjacent layers of upper and lowershell 40, 42 at the periphery of the shell. Sewn shell constructionsknown in the art prevent the power entry from being more peripherallylocated because the periphery includes a stitch line and as a result thepower entry must be located on the flat surface of the shell rather thanthe edge. Locating the power entry on the flat surface of the supportmay result in the patient laying on the hard lump created by the powerentry module and could contribute to the formation of a pressure injury.In some embodiments, the power entry module 130 is a piece of moldedplastic, for example in a shield-shape, that can be sealed between thesheets 42 and 44 in the peripheral bond 48 edge seal of the shells 42,44. The pointed ends of the shield-shaped power entry module 130 allowthe shells 42, 44 to transition smoothly from the area where the upperand lower shells 42, 44 are sealed to each other, to the adjacent areawhere the shells 42, 44 are sealed to the power entry module 130 moduleand then back to the shells 42, 44 being sealed to each other. In someembodiments, the power entry module 130 includes a tubular channeltraversing from the outer side to the inner side of the shell. Thetubular channel may be sized to accommodate the wire cable that containsthe power and sensor wires. The wire cable can pass through the tubularchannel from outside to inside the heated underbody support and can beadhesive, solvent or heat bonded to the power entry module in thisposition, creating a water-tight seal. In another embodiment, the powerentry module 130 may be shaped and sized to house a plug-in connector.

The heater assembly 1 can be encased in a shell of plastic film asdescribed, or may have no shell. With or without a shell or compressiblematerial layer 20, it can be used as a mattress overlay on top of, orcan be inserted into, a pressure reducing mattress. For example, sincepressure reducing mattresses typically have water resistant covers, theheater assembly 1 may be inserted directly into the mattress, inside themattress cover, without a shell on the heater assembly 1. In eithercase, the heated underbody support is designed to have little or nonegative impact on the pressure reducing capabilities of the mattress onwhich it is laying or into which it is inserted.

When used as a mattress overlay, the shell of the heater assembly 1 maybe water resistant, flexible, and durable enough to withstand the wearand tear of operating room use. Examples of materials which may be usedfor the shell include but are not limited to urethane and PVC. Manyother suitable plastic film or fiber-reinforced plastic film shellmaterials are anticipated. In some embodiments, the shell material isbetween about 0.010 and about 0.015 inch thick. In this thickness range,both urethane and PVC, for example, are strong but retain an adequatestretchability. The heated underbody support may cover approximately theentire surface of the surgical table or any other bed. Alternately, theheated underbody support may be sized to fit some or all of the cushionthat forms the support surface of a surgical table. For example, if thecushion has multiple separate sections, such as three, the heatedunderbody support may be sized to fit over one or two or all three ofthe cushion sections.

The heated underbody support may have two or more attachment points suchas tabs 140 for securing the support over the top of a surgical mattressor table such as is shown in FIG. 23. These attachment points may betabs 140 or flaps made from shell material that extend outward from theperipheral bond 48 of the shell. These attachment points may befiber-reinforced and yet flexible and somewhat loose, so that they donot cause hammocking of the shell. The attachment points can be securedto the table with many different means including straps, ties, loops,hooks, snaps, barbs, Velcro or other attachment means.

In an example of an attachment method shown in FIG. 24, there are aseries of barbs 142 extending radially outward from a longitudinallyextending body 144 in the form of a strap, made of rubber or otherflexible material, for example. A loop or aperture 146 extending throughthe strap can engage the side rail of the table and the barbs 142 canengage an aperture 148 in the tab 140 of the heated mattress overlay 2.

In some embodiments, a high tech foam may be included in thecompressible material layer 20 or may be in addition to the layer ofcompressible material 20, to reduce the pressure exerted against thepatient's skin during surgery. High tech foams include but are notlimited to visco-elastic foams that are designed to maximizeaccommodation of the patient into the mattress. As previously noted,accommodation refers to the sinking of the user, such as the patient,into the underbody support until a maximal amount of support surfacearea is in contact with a maximal amount of skin surface, and thepressure exerted across the skin surface is as uniform as possible.These high tech foam materials may accommodate the patient moreeffectively than simple urethane upholstery foam. Unlike prior artmattress heaters or heating materials, the unique stretchable, flexible,free floating design of the heater assemblies 1 described herein allowthem to overlay a layer of visco-elastic foam and maintain theaccommodation properties of the foam. Further, the heater assembly 1 maybe soft, flexible and stretchable enough to be the separated from thepatient by only a single layer of plastic film and still be comfortable.The avoidance of multiple layers of materials interposed between thepatient and the mattress foam maximizes accommodation and heat transfer.

In embodiments comprising heated mattresses 3 including foam layers 150,a water-resistant shell or cover 160 may encase the foam 150 as shown,for example, in FIG. 25. The foam 150 may be simple urethane foam orhigh-tech foam such as visco-elastic foam, for example. The cover 160may be made of plastic film that has been extruded onto a woven fabric(e.g., Naugahyde), for example. In one embodiment, the heater assembly 1may be located within or may be removably inserted directly into themattress cover 160, with or without a shell 40 on the heater assembly 1.The heater assembly 1 may be placed directly on top of the mattress foam150 inside the cover 160 or a heater assembly 1 (with its own shell) maybe placed on top of a mattress outside of the mattress cover 160. If afoam mattress has its own shell, the thickness of the shell 40 of theheater assembly 1 can be reduced to, for example, about 0.003 and about0.010 inch, or even omitted, because the heater assembly 1 is protectedfrom mechanical damage by the cover 160 of the mattress 150. The thinnershell material improves the stretch-ability of the shell. Alternately,the heating element 10 may be bonded directly to the mattress foam 150.

The thermal effectiveness of this heated underbody support can beoptimized when the heating element 10 is overlaying a layer that canprovide maximal accommodation of the patient positioned on the support.In this condition, the heating element 10 is in contact with a maximalamount of the patient's skin surface which maximizes heat transfer.Heated underbody supports made with inflatable air chambers forming orincluded in the compressible material layer 20 or in addition to thecompressible material layer 20, can provide excellent accommodation.Further, a heated underbody support with excellent accommodationproperties having a heating element 10 as described herein avoidsdegrading the accommodation properties of the mattress when a heaterassembly 1 is added. Therefore, the combination of the heater assembly 1design with an accommodating mattress such as a mattress made with oneor more inflatable air chambers 170 as shown in FIG. 26, for example, isadvantageous and synergistic for the effectiveness of both technologies.

An embodiment of a heated mattress 3 comprising one or more air chambers170, 172 and a heater assembly 1 overlaying the one or more air chambers170, 172 is shown in FIGS. 26, 27 and 28. In some embodiments, a singleair chamber 170 or a plurality of elongated inflatable chambers 172 arepositioned under the heater assembly 1. The plurality of elongatedinflatable chambers 172 may be cylindrical in shape and may be orientedin parallel and positioned side-by-side one another, with their longaxes extending substantially from one side of the mattress to the otherside. However, other inflatable chamber shapes and orientations areanticipated. The inflatable chambers 172 may be round or ovoid in crosssection. They may or may not be physically secured to the adjacent airchamber. Alternately, they could be secured to a base sheet or simplypositioned and contained within the mattress cover 160 without beingsecured. The chambers 170, 172 may be made of a fiber-reinforced plasticfilm or a plastic film that has been bonded, laminated or extruded ontoa woven or non-woven fabric reinforcing layer. Urethane may be used asthe plastic film, but other plastic film materials are anticipated.Woven nylon may be used as the reinforcing layer, but other fabricmaterials are anticipated.

The inflatable chamber 170 or chambers 172 can be sealed and static, orconnected together in fluid connection to allow redistribution of airbetween the chambers 172. In some embodiments, the chamber 170 orchambers 172 can be actively inflated and deflated while the heatedmattress 3 is in use. The inflatable chambers 172 may be inflated anddeflated each independently, all simultaneously, or in separate groups,while the heated mattress 3 is in use. In some embodiments, the chambers172 are each a part of two separate groups and may be segregated forexample by every other chamber 172 (alternating chambers 172) accordingto their relative side-by-side positions. A conduit or conduits may bein separate independent fluid communication with each chamber 172 of thegroup of inflatable chambers for independently introducing or removingair from that group of inflatable chambers.

Alternately, there may be only a single group of chambers 172 or theremay be more than two groups of chambers 172 which can be separatelyinflated or deflated. If multiple groups of chambers 172 are used, theymay or may not be evenly or symmetrically arranged. For example, chambergroups may be separated according to the amount of weight-bearingassociated with that area. For example, chambers 172 in greater weightbearing areas, such as the torso and hips, may be in a first group,while chambers 172 in areas bearing less weight, such as thosesupporting the head and legs, may be a separate group of chambers 172.In this way, the lighter portions of the patient's body may be supportedby chambers 172 that are inflated to a lower air pressure than chambers172 that support more weight/heavier body portions.

Chambers 172 may be secured to the adjacent chamber or to a base sheetor may be secured by the ends to an element running along each side ofthe mattress 3, and in some embodiments the chambers 172 and theirconnectors for fluid connection may be individually detachable. In thisinstance, if a single chamber 172 or connector fails or is damaged, itcan be replaced without requiring the replacement of the entireinflatable heated mattress 3.

The material forming the chamber 170 or chambers 172, such as a plasticfilm, may be bondable with RF, ultrasound, heat, solvent, or otherbonding techniques. The film or film layer of the laminate may be foldedback on itself and a single longitudinal and two end bonds may cooperateto form an inflatable chamber 170, 172. More complex chamberconstruction and bonding embodiments are anticipated.

The conduit fluid connection for air flow to and from and between theinflatable chambers 172 may be plastic tubing, for example. The inletinto the inflatable chamber 172 can be through one of the bonded seamsor may be through a surface of the chamber 172. To prevent occlusion ofthe tubing at the inlet, the tubing may extend one or more inches intothe chamber. Other conduits are anticipated, such as a molded orinflatable plenum that may run the length of the heated mattress 3.

In some embodiments, a heater assembly 1 (such as a heater assembly 1encased within a water resistant shell) is placed on top of theinflatable chambers 170, 172 so that the conductive fabric heatingelement 10 is at or near the top surface of the heated mattress 3.Alternately, a heater assembly 1 (without a shell) could be placed ontop of the inflatable chambers 170, 172 so that the heating element 10is at or near the top surface of the mattress. The heated mattress 3 mayinclude a flexible, water resistant cover 160 that encases the heaterassembly 1 and the inflatable chambers 170, 172.

In some embodiments, the water resistant mattress cover 160 is a plasticfilm laminated or extruded onto a woven or knit fabric such as“Naugahyde.” This construction is soft and durable. Alternately, thecover 160 can be made of plastic film, fiber-reinforced plastic film ora plastic film laminated or bonded to a woven, non-woven, or knitfabric.

The heater assembly 1 of the heated mattress 3 may be “free floating”within the water resistant cover 160 of the heated mattress 3.Alternately, the heater assembly 1 may be attached to the chamber 170 orchambers 172 or foam 150 or attached to the cover 160, either at theedges of the heater assembly 1 or on or across the top or bottom surfaceof the heating element 10.

One or more edges of the heater assembly 1, such as two or four edges,may be attached to the ends of the elongated inflatable chambers 172 bysnaps, Velcro or any other suitable forms of attachment. Suchembodiments maximally stabilize the heater assembly 1 within the heatedmattress 3. A series of independent securing tabs or flaps may extendlaterally from the bonds 48 of the heating unit shell 40. Where 2 to 4tabs 140 may be sufficient to secure the heater assembly 1 to a surgicaltable as a mattress overlay, a series of tabs 40 that correspond withsome or all of the inflatable chambers 172 may be desirable foranchoring the heater assembly 1 inside the inflatable heated mattress 3.As the inflatable chambers 170, 172 inflate and become turgid, theysimultaneously stretch the heater assembly 1 laterally, assuring thatthe heating element 10 cannot wrinkle and fold on itself or becomedisplaced.

The inflatable heated mattress 3 may include pressure sensor assembliescapable of detecting in real time the actual internal air pressure ofthe inflatable chambers 170, 172 and may also include a comparator whichmay be in operational communication with the controller for comparing adesired internal air pressure value of the inflatable chambers 170, 172with the actual internal air pressure, and a pressure adjustingassembly, also in operational communication with the controller, foradjusting the actual internal pressure. The controller may be activatedby active feedback data derived from the comparator for maintaining adesired internal pressure value in the inflatable chambers 170, 172 byadjusting the amount of inflation of the inflatable chamber 170 or ofthe groups of inflatable chambers, such as first and second groups ofinflatable chambers 172.

The controller may be operationally connected to a first conduit and asecond (or multiple) conduit and a pump for inflating the air chamber170 or plurality of inflatable chambers 172. Each chamber 172 orplurality of chambers 172 may be independent of each other chamber 172so that each chamber 172 may react to air pressure changesindependently, or may be connected as a group and may react in concertwith the air pressure changes in the other chambers 172 of the group.The air may be redistributed within the chambers 172 and the interfacepressure may be maintained at any point on the top surface of each ofthe plurality of chambers 172 which is engaged with an anatomicalportion of the user's body, at an average pressure below a capillaryocclusion pressure threshold of 32 mm Hg, for example.

The optimal air pressure in the chambers may be predetermined, forexample, at a pressure between about 0.4 and about 0.6 psi. Thecontroller may add to or release air from the chambers, in order tomaintain a stable and constant pressure in the chambers when themattress is loaded with a patient. The predetermined pressure may beprogrammed into the controller or it may be selected by the operator.

Alternately, the controller may include an algorithm for determining theoptimal air pressure in the chambers 170, 172, for each patient size,shape, weight and position, to achieve the maximal accommodation of thepatient into the air chambers. Maximal accommodation occurs when thechambers 170, 172 are collapsed to a point where a maximal surface areais in contact with the patient and yet the protruding areas such as thepatient's butt in the supine position or the hip and shoulder in thelateral position, are not “bottoming out” against the table below orother surface beneath the mattress. If the chambers 170, 172 areinflated more than is needed to support the patient, the patienteffectively would be laying on the uppermost part of each over-inflatedtubular chamber and is supported by a relatively small surface area. Ifthe chambers 170, 172 are deflated too much, protruding parts of thepatient would “bottom out” and be resting on the table or other surface.Both of these conditions result in significant and potentially dangerouspressure being applied to the patient's skin. The optimal air pressureis somewhere in between these two extremes, where the patient in thegiven position is maximally accommodated into the chamber without“bottoming out,” effectively floating.

One way to determine the amount of air pressure that is optimal formaximum accommodation is to inflate the chambers to a pressure that isexpected to be greater than the optimal pressure, for example 1.0-1.5psi. Then the air is released slowly, such as in increments, allowingtime between each release for equilibration of the air in the chamber170 or groups of chambers 172 if necessary, and an accurate measurementof the static air pressure in the chambers 170, 172 is then taken. Theair release increment may be determined by the duration of time that airis released, for example 2-5 seconds. Alternately the air releaseincrement may be determined by a measured volume of air released. Theair release increment may be determined by a combination of time andpressure used to calculate and standardize the volume of air releasedwith each increment. In some embodiments, the duration of air releaselengthens as the air pressure decreases resulting in relatively similarvolumes of air being released with each increment.

An algorithm which may be used by the controller to determine optimalair pressure, plots the curve of pressures for each sequential airrelease. The resulting plot has two phases: a first phase wherein themeasured pressures decrease relatively rapidly and a second phasewherein the measured pressures decrease relatively slowly. The part ofthe curve represented by the first phase has a steeper downward slopeand the part of the curve represented by the second phase has a moregradual downward slope. The first phase generally represents theover-inflated chambers with the patient supported by a relatively smallupper surface area of the chamber. The second phase generally representsthe patient sinking into the gradually collapsing chambers, whereinlittle additional surface area is enlisted with each additionalincremental deflation. In the second phase, the patient is effectively“floating” to the maximal extent of the mattresses ability toaccommodate the patient.

The controller can identify the pressure at which the pressure changetransitions from the steep downward slope of the first phase, to thegradual downward slope of the second phase. The second phase may beidentified by identifying a decreased or minimal pressure drop betweentwo sequential air releases. For example, if a decrease of less thanabout 10% is detected between two sequential air releases, thecontroller may then stop the air releases and maintain that pressure asthe optimal pressure. Depending on the design and sizes of the chambersand the amount of air released in each increment, the pressure dropindicating that the pressure is at the optional pressure may be lessthan from about 2 to 15% between increments, and may be identified bythe air pressure drop between increments being significantly less thanthe air pressure drop in the first phase. When the second phase is firstidentified by recording a reduced or minimal pressure drop betweensequential air release increments, the air pressure is near the optimalpressure and the controller may be programmed to maintain that airpressure. Alternately, when the first minimal difference in airpressures are detected with a subsequent air release, the controller maybe programmed to release an additional predetermined amount of air or tore-inflate the air chamber with a predetermined amount of air.

A controller which may be used in various embodiments is shown in FIG.29. The controller 182 may be included in a console 180. A shut offtimer 184 and a power supply 186 may each be operatively coupled to thecontroller 182, meaning that the shut-off timer 184 can be a separatecomponent, or the shut-of timer 184 and the controller 182 can have anyother suitable functional relationship. The temperature sensor assembly110 and over-temperature sensor assembly 115 can be configured toprovide temperature information to the controller 182, which may act asa temperature controller. The controller may function to interrupt suchpower supply (e.g., in an over-temperature condition) or to modify theduty cycle to control the heating element 10 temperature. In embodimentsincluding an inflatable support, an air pressure comparator (not shown)may be in operatively coupled to the controller 182, meaning, like theshut-off timer 184, the air pressure controller can be a separatecomponent, or the air pressure controller and the controller 182 canhave any other suitable functional relationship. The air pressure sensorassemblies can be configured to provide air pressure information to thecontroller 182, which may act as an air pressure controller.

In the foregoing detailed description, the invention has been describedwith reference to specific embodiments. However, it may be appreciatedthat various modifications and changes can be made without departingfrom the scope of the invention as set forth in the appended claims.

1. A heated underbody support comprising a heated mattress, heatedmattress overlay, or heated pad, the heated underbody supportcomprising: a heater assembly comprising: a flexible heating elementcomprising a sheet of conductive fabric having a top surface, a bottomsurface, a first edge and an opposing second edge, a length, and awidth, wherein the sheet is comprised of threads separately andindividually coated with an electrically conductive or semi-conductivematerial, and wherein the coated threads of the fabric are able to sliderelative to each other such that the sheet is flexible and stretchable;a first bus bar extending along the entire first edge of the heatingelement, the first bus bar adapted to receive a supply of electricalpower; a second bus bar extending along the entire second edge of theheating element; and a temperature sensor; and a layer of compressiblematerial adapted to conform to a person's body under pressure from aperson resting upon the support and to return to an original shape whenpressure is removed, the layer located beneath the heater assembly andhaving a top surface and an opposing bottom surface, a length, and awidth, wherein the length and width of the layer are approximately thesame as the length and width of the heater assembly.
 2. The heatedunderbody support of claim 1 wherein the conductive or semi-conductivematerial comprises polypyrrole.
 3. The heated underbody support of claim1 wherein the compressible material comprises a foam material.
 4. Theheated underbody support of claim 1 further comprising a water resistantshell encasing the heater assembly, the shell comprising an upper shelland a lower shell that are sealed together along their edges to form abonded edge, wherein the heater assembly is attached to the shell onlyalong one or more edges of the heater assembly.
 5. The heated underbodysupport of claim 1 wherein the compressible material comprises one ormore flexible air filled chambers.
 6. The heated underbody support ofclaim 1 wherein the heating element has a planar shape when not underpressure, wherein, in response to pressure, the heating element isadapted to stretch into a 3 dimensional compound curve without wrinklingor folding while maintaining electrical conductivity, and wherein theheating element is adapted to return to the planar shape when pressureis removed.
 7. A heated underbody support comprising a heated mattress,heated mattress overlay, or heated pad, the heated underbody supportcomprising: a heater assembly comprising: a flexible heating elementcomprising a sheet of conductive fabric having a top surface, a bottomsurface, a first edge and an opposing second edge, a length, and awidth; a first bus bar extending along the first edge of the heatingelement, the first bus bar adapted to receive a supply of electricalpower; a second bus bar extending along the second edge of the heatingelement; and a temperature sensor; wherein the heating element has aplanar shape when not under pressure, wherein, in response to pressure,the heating element is adapted to stretch into a 3-dimensional compoundcurve without wrinkling or folding while maintaining electricalconductivity, and wherein the heating element is adapted to return tothe planar shape when pressure is removed; and a layer of compressiblematerial which conforms to a patient's body under pressure and returnsto an original shape when pressure is removed, wherein the layer ofcompressible material is located beneath the heater assembly.
 8. Theheated underbody support of claim 7 wherein the flexible heating elementcomprises a fabric coated with a conductive or semi-conductive material,the conductive or semi-conductive material comprising a carbon fiber ormetal containing polymer or ink.
 9. The heated underbody support ofclaim 7 wherein the flexible heating element comprises a fabric coatedwith a conductive or semi-conductive material, the conductive orsemi-conductive material comprising a polymer.
 10. The heated underbodysupport of claim 7 wherein the compressible material comprises a foammaterial.
 11. The heated underbody support of claim 7 wherein the heaterassembly is attached to the top surface of the layer of compressiblematerial.
 12. The heated underbody support of claim 7 further comprisinga water resistant shell encasing the heater assembly, the shellcomprising an upper shell and a lower shell that are sealed togetheralong their edges to form a bonded edge.
 13. The heated underbodysupport of claim 12 wherein one or more edges of the heater assembly aresealed into the bonded edge.
 14. The heated underbody support of claim12 wherein the heater assembly is attached to the upper layer of waterresistant shell material.
 15. The heated underbody support of claim 12wherein the heater assembly is attached to the shell only along one ormore edges of the heater assembly.
 16. The heated underbody support ofclaim 12 further comprising an electrical inlet, wherein the inlet isbonded to the upper shell and the lower shell and passes between them atthe bonded edge.
 17. The heated underbody support of claim 7 wherein thecompressible material comprises one or more flexible air filledchambers.
 18. The heated underbody support of claim 7 wherein theheating element has a first Watt density when in a planar shape and asecond Watt density when stretched into a 3 dimensional compound curve,and wherein the first Watt density is greater than the second Wattdensity.
 19. The heated underbody support of claim 7 wherein thetemperature sensor for monitoring a temperature of the heating elementin located in contact with the heating element in a substantiallycentral location upon which a patient would be placed during normal useof the support.
 20. The heated underbody support of claim 7 furthercomprising a power supply and a controller for regulating a supply ofpower to the first bus bar.
 21. A heated underbody support comprising aheated mattress having a first end and a second end, the heatedunderbody support comprising: a heater assembly comprising: a flexibleheating element comprising a sheet of conductive fabric having a topsurface, a bottom surface, a first edge and an opposing second edge, alength, and a width; a first bus bar extending along the first edge ofthe heating element; a second bus bar extending along the second edge ofthe heating element; at least one temperature sensor; the first bus baris adapted to receive electrical power from a power supply; wherein theheating element has a planar shape when not under pressure, wherein, inresponse to pressure, the heating element is adapted to stretch into a3-dimensional compound curve without wrinkling or folding while maintainelectrical conductivity, and wherein the heating element is adapted toreturn to the planar shape when pressure is removed; a layer ofcompressible material which conforms to a patient's body under pressureand returns to an original shape when pressure is removed, wherein thelayer of compressible material is located beneath the heater assembly;an inflatable chamber positioned under the layer of compressiblematerial; and a flexible, water resistant cover that encases the heaterassembly, the layer of compressible support material and the inflatablechamber.
 22. The heated underbody support of claim 21 further comprisingone or more additional inflatable chambers positioned under the layer ofcompressible material, wherein each of the inflatable chambers areelongated and have a longitudinal axis and are positioned side-by-sideone another with their longitudinal axes extending substantially fromthe first end to the second end of the support.
 23. The heated underbodysupport of claim 21 further comprising one or more additional inflatablechambers, wherein the inflatable chambers can each be inflated anddeflated independently while the support is in use.
 24. The heatedunderbody support of claim 21 further comprising one or more additionalinflatable chambers, wherein the inflatable chambers can all be inflatedand deflated simultaneously as a group while the support is in use. 25.The heated underbody support of claim 21 further comprising one or moreadditional inflatable chambers, wherein the inflatable chambers can beinflated and deflated in two or more groups while the support is in use.26. The heated underbody support of claim 25 wherein the inflatablechambers can be inflated and deflated in two groups while the support isin use, and wherein the inflatable chambers are in alternating groupssuch that each inflatable chamber is in a different group from eachinflatable chamber which is beside it.
 27. The heated underbody supportof claim 21 further comprising one or more additional inflatablechambers, each of the inflatable chambers belonging to one of two ormore groups, and further comprising separate conduits to each group,each conduit providing independent fluid communication one groups ofinflatable chambers for independently introducing or removing air fromthat group of inflatable chambers.
 28. The heated underbody support ofclaim 27 further comprising: a pressure sensor for measuring an actualinternal air pressure of the groups of inflatable chambers; and acontroller including a comparator for comparing a desired internal airpressure for each group of inflatable chambers with the actual internalair pressure of each group inflatable chambers, the controlleroperatively connected to each of the conduits and to an air pump, thecontroller further including a pressure adjusting assembly for adjustingthe actual internal pressure; wherein the controller is adapted to causeinflation or deflation of each group of inflatable chambers to adjustthe actual internal air pressure of each of the group of inflatablechambers toward the desired internal air pressure.
 29. The heatedunderbody support of claim 27 wherein each inflatable chamber withineach inflatable chamber is in fluid connection with every otherinflatable chamber of its own group so that each air pressure changes inone inflatable chamber redistribute to all of the other inflatablechambers in the same group; and wherein the an interface pressure ismaintained on a top surface of each group of chambers at a locationwhich supports a patient's body during normal use, the interfacepressure being below a capillary occlusion pressure threshold of 32 mmHg.
 30. The heated underbody support of claim 21 further comprising ashell comprising two sheets of flexible surrounding the heater assembly,the shell comprising a water resistant plastic film or fiber reinforcedplastic film, wherein the two sheets are sealed together near the edgesof the heater assembly.
 31. The heated underbody support of claim 21including a power supply and controller for regulating the supply ofpower to the first bus bar.
 32. A method of warming a person comprising:positioning the person on a heated underbody support comprising a heatedmattress, heated mattress overlay, or heated pad, the heated underbodysupport comprising: a heater assembly comprising: a flexible heatingelement comprising a sheet of conductive fabric having a top surface, abottom surface, a first edge and an opposing second edge, a length, anda width; a first bus bar extending along the first edge, the first busbar adapted to receive a supply of electrical power; a second bus barextending along a second edge; a temperature sensor near the heatingelement; wherein the heating element has a planar shape when not underpressure, and wherein, in response to pressure from the personpositioned on the support, the heating element stretches into a 3dimensional compound curve without wrinkling or folding while maintainelectrical conductivity; a layer of compressible material locatedbeneath the heater assembly; and a flexible water resistant shellencasing the heater assembly; activating the support; and directing thesupport to maintain a desired temperature.